216 



REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



or hermaphrodite, according to the organs 

 which they contain. The male concepta- 

 cles present in their interior an arrangement 

 of branched filaments, or hair-like organs, 

 which, taking their origin from the surrounding 

 cellular tissue, converge towards the pore. 

 At the summits of these filaments, the so- 

 called antheridia are supported, which consist 

 of little ovoid transparent vesicles. They 

 contain, in their early condition, a granular 

 protoplasmic material, but as they approach 

 maturity, the so-called antherozoids make 

 their appearance. These last are hyaline 

 corpuscles, not exceeding about -g-oVo ^ an 

 inch in their longest dimension. Each con- 

 tains a granule of a greyish or reddish orange 

 colour, from which the organs of locomotion 

 emanate. The form of the zoids differs ac- 

 cording tothegenus. InFucus, they are bottle- 

 shaped, and each possesses a pair of cilia, one 

 of which, the shortest, is directed forwards 

 from the neck, while the longest emanates 

 from the coloured point and is pointed hack- 

 wards. In Halidrys, the zoid is ovoid or 

 spherical, and the longest cilium is directed 

 forwards. In Fucus and several other genera, 

 the transparent vesicle in which the zoids are 

 immediately contained, is itself enclosed in a 

 second of similar form. At the period of 

 maturity this last gives way at its apex : the 

 internal sack is expelled, and at once finds 

 its way towards the external opening. In 

 the meantime its delicate membrane disap- 

 pears, and the liberated zoids commence their 

 active motions. 



9. Although the antherozoids of the Fu- 

 coideas differ from the zoospores of tlie other 

 olive-coloured Algae, in their not possessing the 

 power of germination, there are yet remarkable 

 points of correspondence between them, in 

 their form, structure, and mode of develop- 

 ment. Both are composed of a hyaline pro- 

 toplasms, and the position of the coloured 

 granule, as well as the arrangement of the cilia, 

 corresponds. They differ, in the first place, in 

 size, and secondly, in respect of the chlovo- 

 phylle granules, which are present in the zo- 

 ospore, but absent in the antherozoid. As 

 regards the question of their functional sig- 

 nification, they may be considered, on the 

 one hand, as the elements of a male secretion, 

 and the organs in which they are contained, 

 as antheridia ; on the other, we may look 

 upon them as the formal representatives 

 of structures destine^ in other families to 

 the performance of functions of which they 

 are themselves incapable. In favour of the 

 first of these views we have no direct evi- 

 dence, and must trust entirely to analogy. 

 We know that in Cutleria and its allies, 

 the zoospores display the power of germi- 

 nating without the slightest reference to the 

 presence or absence of the secretion of the 

 supposed male organ. Further, if, as all obser- 

 vations which have been hitherto made, tend 

 to prove, the zoospores of all the green Algae, 

 and of so many of the olive-coloured, normally 

 germinate under the condition of the constant 

 non-existence of such organs, it is difficult 



to see why an exception should be made in 

 favour of those of other families in which 

 they are present. As regards the Fucoideae, 

 we have certainly no evidence whatever that 

 the antheridia perform any function, either 

 more or less important in the reproductive 

 process. 



10. In the family of Vaucheriaceae, the zoo- 

 sporous reproduction is remarkably modified by 

 the substitution of a single multiple zoospore, 

 of large size, for a number of smaller ones. 

 The frond of Vaucheria consists of a branched 

 tube, and much resembles in general form, 

 that of the Bryopsideae, from which the Vau- 

 cheriae in their vegetative condition Jitter only 

 in respect of the arrangement of the chloro- 

 phylle. The commencement of the formation 

 of zoospores is announced by the condensa- 

 tion of the green protoplasma in the rounded 

 terminations of the branches of the plant. 

 This condensation is accompanied with an 

 enlargement of the cylindrical filament, which 

 soon appears club-shaped, and is completely 

 occupied by a confused and opaque dark -green 

 mass. Shortly afterwards a septum is formed, 

 which limits the terminal portion of the tube. 

 Within the separate cavity thus formed, the 

 mass of protoplasma becomes further con- 

 densed; its margin being surrounded by a clear 

 space which intervenes bet ween its external sur- 

 face and the tube membrane. This body, which 

 possesses an oval form, is the future zoospore. 

 No sooner is it completely developed than the 

 membrane which encloses it gives way at the 

 apex, and it begins to insinuate itself through 

 the resulting narrow opening. Having com- 

 pletely freed itself, it forthwith commences an 

 active progressive motion, which is accom- 

 panied by a circumvolution round its axis. 

 The zoospore at this period possesses no dis- 

 tinct or consistent investing membrane, as is 

 evident from the fact, that if, during its escape, 

 it divides accidentally into two a circum- 

 stance which not unfrequently happens, from 

 the relative narrowness of the opening through 

 which it has to pass each part is complete 

 in itself and capable of germination. Its whole 

 surface is covered with vibratile cilia, which 

 are apparently connected with an epithelium- 

 like structure. In this arrangement there 

 seems to be an indication of a tendency to a 

 division into smaller particles, by the melting 

 together of a number of which the whole 

 may be conceived to be formed. Like all zo- 

 ospores its period of active motion is short; it 

 soon becomes stationary and begins to germi- 

 nate.* The zoospores of Vaucheria seem to 

 correspond closely with the motionless spores 

 of the true Dictyotaceae (Dictyota, Padina, 

 &c.), as well as with those of the Fucaceae. 

 In the case of the latter, the accuracy with 

 which their structure and germination have 

 been studied, has enabled us to follow out the 

 analogy more closely. In speaking of the an- 



* See Thuret, Ann. des Sc. Nat. 2" S. xix. 269 ; 

 Vaucher, Hist, des Conferves d'Eau douce, p. 246 ; 

 Karsten, Die Fortpflanzung der Conferva fontinalis, 

 Bot. Zeit. 5 Stiick, 1852. 



