صور الصفحة
النشر الإلكتروني

by passing through holes in the membrane of the oogonium, a mode of access which we have already seen to occur in Sphæroplea.

We must not part with the Zoosporeæ without mentioning the observations of M. Cohn and Mr. H. J. Carter* on reproduction in the Volvocinew. Although these two writers are at variance with regard to the monacious or diæcious nature of Volvox globator (the species which has received the greatest amount of attention) there seems no reason to doubt that the sexual process corresponds exactly with that which has been observed in other Algæviz., That it consists in the impregnation by spermatozoa of a previously membraneless “primordial spore.”

In the Florideæ the knowledge of the phenomena of impregnation is far less advanced than in the other two divisions. The organs of fructification are of three kinds, 1st, the tetraspores consisting of an oblong or globular external cell enclosing four spores, each of which is capable of germination and of reproducing the plant directly ; 2nd, antheridia, containing corpuscles which have been regarded as spermatozoa, but the nature of which is as yet extremely doubtful.

It is stated in Mr. Berkeley's Introduction to Cryptogamic Botany, that the plants of this division produce antheridia filled with active spermatozoa; but although some observations to this effect have been recorded by Derbès and Solier, they have not been confirmed by other botanists. Dr. Pringsheim, at the meeting of German Naturalists at Bonn, in the year 1857 (a report of which is to be found in the Botanische Zeitung for 1857, p. 784), unhesitatingly denies the existence of spiral or motile filaments. Since that time Dr. Gustav Venturi has describedt certain organs occurring in Wrangelia penicillata, Polysiphonia elongata, and Callithamnion vesicolor, which have the appearance of being antheridia. He did not, however, find true spermatozoa, although in Callithamnion versicolor the upper cells of the so-called antheridia contained minute cellules in which slight movements were observed, but which movements might possibly have been only molecular.

“ Thirdly, besides the tetraspores and the so-called antheridia, the Florideæ produce spores grouped in definite masses, and usually, but

• See Annales Sc. Nat. 4 Ser., Vol. v. p. 323. Ann. and Mag. of Nat. Hist. Jan. 1859.

† See “ Beobachtungen über die Fructifications-organe der Florideen." Wien z. B. V. Vol. x. p. 583.

not always, enclosed in special cells or conceptacles. M. Pringsheim long since suggested* that these conceptacular spores, called cystocarps by Nägeli, are either true female sexual organs, or that they produce, like the spores of ferns, an organ which performs in some way the female sexual functions. It would seem, however, that he has since seen reasons for changing this opinion, for in the Botanische Zeitung (loc. cit.) he is reported to say that the conceptacular fruit does not differ essentially from the tetraspores; that it is, in fact, only a more divided form of the latter; that in Ptilota plumosa the transition from one to the other may be followed out; and that the spores often germinate within the capsule, in which case impregnation is out of the question. In a paper on the Ceramiaceæ in the Reports of the Bavarian Academy,t Nägeli has some observations on the nature of the fruit of the Florideæ. They occur in the course of some comments upon a proposed subdivision of the Order by J. Agardh, who separated two groups, viz. the Spyridieæ and the Wrangelieæ, on the ground of the different formation of their cystocarps. Nägeli says: “ In most Florideæ both cystocarps and tetra"spores are found; in some, however, the one or the other kind " of fruit is wanting. Their physiological import is still uncertain. “I have expressed the opinion that the tetraspores are the "female fruit, and that they are impregnated by the antheridia; * the cystocarps, on the other hand, are the asexual germs. Up " to this time, I find no reason to give up this opinion, and until “it is confirmed or set aside, it is for many reasons the most "probable. Irrespective of the striking resemblance between

the cystocarps, and the gemmæ and receptacles of the mosses and liverworts, two points relative to the Ceramiaceæ may be mentioned. In the first place, the tetraspores and the antheridia are constant in their relative position, and therefore agree in their morphological signification, whilst the cystocarps vary. The

second circumstance to be noted is the distribution of the three " reproductive organs upon different individuals. Trieciousness is " most usual, so that one plant bears only antheridia, another only “ tetraspores, a third only cystocarps. Exceptionally, however,

* See Ann. des Sc. Nat. 4 Ser. Vol. fii. p. 376.

† Beiträge zur Morphologie und Systernatik der Ceramiaceæ. Sitzungsberichte der konigl. Bayerischen Acad. der Wiss. zu München ; Jahrgang 1861. Band ii. p. 297.

“ tetraspores and cystocarps occur upon the same plant, as has been “ seen by the MM. Crouan in a species of Callithamnion; antheridia “and cystocarps have been seen by Bornet upon Lejolisia ; and “ antheridia and cystocarps have also been seen by myself upon “ Callithamnion bipinnatum, Crouan, and Herpothamnion hermaphroditum, Nägeli. These observations point to the fact that the Florideæ “ are normally diæcious, and that the plants with cystocarps may “ really be male and female individuals, in which, for the support of " the neutral organ, the formation of the sexual organs (antheridia “ and tetraspores) has been suppressed.

“If my opinion as to the nature of the cystocarps is correct, " they might possibly be wanting in certain Florideæ, whilst the tetra“spores must occur in all. It might be objected that there are “probably more Florideæ, in which the tetraspores are unknown than “ in which the cystocarps are unknown. This, however, is not con“clusive, inasmuch as the former are usually invisible to the naked "eye, whilst the latter are easily seen and collected. There are some " Ceramiaceæ very generally distributed, and occurring in places “ where indefatigable algologists reside, in which tetraspores have “ been found, but no cystocarps have yet been observed, e g. Rhodochor. ton Rothii and R. floridulum and Antithamnion cruciatum.

The result at which Professor Nägeli arrives is that the cystocarps ought not, in the classification of the Ceramiaceæ, to be used even for subordinate divisions ; and if he is right in his views they must be considered as asexual organs of very little importance. Whether botanists will accept this conclusion time alone can show. At present we can only say, as M. Vaillant has remarked in his recent work, * that the notions of botanists as to the Florideæ are very undefined, and that although the nature of their organs may lead to the supposition of sexuality, further observations are indispensable before the existence of male and female Florideæ can be looked upon as any. thing more than a vague supposition.

We must not close this report without referring to the disputed question as to the nature of the conjugation which takes place in the Zygnemaceæ and other allied Algæ. As far as we are aware it is not yet settled whether this conjugation is a sexual process. We cannot here discuss the point, and must refer those who are interested in the question to Dr. De Bary's Essay, “ Untersuchungen über die

• "De la fecondation dans les Cryptogames," p. 53.

Familie der Conjugaten," and particularly to the second chapter “Ueber die Bedeutung der Copulation und ihre Verbreitung."

NOTE. Since this report went to press we have seen a paper by Sollman in the Botanische Zeitung for September 2, 1864, in which that author professes to have discovered a true process of impregnation in Nectria Lamyi, De Not. Without venturing any opinion as to the correctness of his observations, we append the conclusions with which he sums them up. He says:

1. Nectria Lamyi has a manifest mycelium, out of which the stroma is formed, and upon the latter the perithecia are developed.

2. The perithecia consist of three layers of cells. The innermost layer is the fructifying layer.

3. Upon this layer, in young perithecia, are situated the processes which bear the spermatia, and which, after the spermatia are separated from them, become developed into paraphyses.

4. The spermatia penetrate the fructifying layer, and reach the cavity of the rudimentary asci, which are in process of development.

5. In the double-walled asci eight cytoblasts originate, into which the spermatia penetrate and amalgamate with their contents, 80 as to form a uniform mass.

6. After the penetration of the spermatia the cytoblast assumes a visible smooth membrane, and becomes a spore capable of reproducing the plant.

7. The species of Nectria are hermaphrodite.

8. The bodies supposed to be granules of protoplasm in the young asci of Sphæriæ, are the particles of disintegrated spermatia.

9. They effect the impregnation of the spores.

[ocr errors][merged small]


WITH NOTES ON THE RECENT SPECIES. By W. Boyd Dawkins, B.A. Oxon. F.G.S. Geological Survey of Great Britain.

INTRODUCTION. § I. Recent Species.-A. 7. striata.-B. H. brunnea.-C. H. crocuta. (p. 80.) $ II. Fossil Species. (p. 82.)

§ III. I. spelæa.-A. Milk Molar Dentition.-B. Comparative measurements of Milk Teeth. - C. Succession of permanent Teeth.-D. Upper permanent Dentition. --E. Lower permanent Dentition. (p. 83.)

$ IV. H. brunnea, Fossil in Britain ? (p. 94.) $ V. H. spelæa, a true H. crocuta. (p.95.)

§ VI. „Table of Comparative Measurements of Permanent Dentition of Recent and Fossil Species. (p. 95.)

In the course of the determination of the vast quantity of organic remains from Wookey Hole Hyæna-den,* upwards of 200 jaws and 500 teeth of Hyæna spelæa of all ages, and showing considerable variations from the typical form, passed through my hands. My only excuse for adding the following notes about them, to a literature already so bulky, is that they clear up some of the doubtful points in the researches of MM. Croizet and Jobert, Marcel de Serres, De Blainville, and others, relative to the value of certain differences assumed to be specific in the milk and permanent dentition of the Spelæan Hyæna. Before, however, I can enter upon these, I must briefly run over the differences which obtain in the dentition of the three existing species of the Genus.

§ 1. The genus Hyæna is characterized by a dental formula, intermediate between the Canidæ on the one hand, and the Felidæ on the other, the deciduous series consisting of

of I. 3. C. 1. Dm. 3. and ones w idmg 01 1. 3. C. 1. Dm. 3., and . I. 3. C. 1. Pm. 4. M. 1. permanent of 1. 3. C. 1. Pm. 3. M. 1.

A. Of the three species into which it is divided, the most common, ranging through North Africa, Asia Minor, Arabia and Persia, and extending down to the Cape, H. striata, Zimmer. (H. vulgaris, Cuv.),

* See two papers by the Author. Quart. Journal Geol. vol. xvii. p. 115, vol. xix. p. 260.

« السابقةمتابعة »