REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



theridia ($ 8.), we described the general 

 form of the conceptacles. In the monoecious 

 and dioecious Fuci, the female conceptacles 

 are distinguished from the male by their olive 

 colour. The spores are developed each in 

 the interior of a perispore, which is borne on 

 a pedicle emanating from the inner wall of the 

 conceptacle. They make their escape by the 

 rupture of the perispore at its apex. At the 

 moment at which this takes place, the spore 

 is perfectly simple, except that in one or two 

 species the surface is covered with cilia, which 

 seem to resemble those of Vaucheria. Soon 

 afterwards, a remarkable series of changes 

 occurs, consisting in the splitting of the en- 

 dochrome into a number of masses usually 

 eight each of which becomes isolated, and 

 finally assumes the form of a smooth and 

 spheroidal sporule, provided with an investing 

 membrane. About twenty-four hours after the 

 completion of this process, germination com- 

 mences. It consists in the budding out of the 

 membrane of each sporule, at some point of 

 its surface, into a nipple-shaped projection, 

 which in the following forty-eight hours, elon- 

 gates into a cylindrical tube; shortly afterwards 

 the whole body of the sporule is converted by 

 repeated division into a mass of cells, in which 

 condition it has been by many writers mis- 

 taken for the original spore, and described as 

 such. The Vaucheria? present the peculiarity 

 of a double mode of reproduction. In the 

 earlier periods of the growth of the plant, 

 there occurs the successive formation of aggre- 

 gate zoospores of large size at the termination 

 of the branches, as above described. In the 

 older fronds these are no longer observed, their 

 place being taken by organs producing germs 

 which are capable of retaining for a long period 

 their power of development. 



11. In that most remarkable plant the Sa- 

 prolegnia ferox, which is structurally so closely 

 related to Vaucheria, though separated from 

 it by the absence of green colouring matter, 

 we find a corresponding analogy in the history 

 of the development. Its vegetative life is, in 

 fact, divisible into two well-marked periods, 

 each characterised by a special mode of germ- 

 formation. During the first, the only one 

 with which we have at present to do, swarms 

 of zoospores which rapidly succeed each other, 

 are formed at the closed terminations of the 

 cylindrical filaments. The mode of their 

 origin, agrees with that of the aggregate zoo- 

 spore of Vaucheria. The protoplasma accumu- 

 lates in the swollen extremity of the filament, 

 and a septum is formed in exactly the same 

 manner as in that plant ; while the mass of 

 protoplasma is now observed to be limited by 

 a distinct surface. At this point the resem- 

 blance ceases ; the protoplasmic membrane 

 divides, just as in the spore-cases of the zo- 

 osporous Algae, into particles, which, as the 

 period of maturity is approached, become more 

 and more easily distinguishable from each 

 other. These particles are the future zo- 

 ospores. Soon they detach themselves from 

 their connection with the membrane which 

 encloses them, and with each other, and pre- 



217 



sent the globular or ovoidal form characteristic 

 of their perfect condition. In the meantime 

 the external tube membrane buds out at its 

 apex, so as to form a conical projection; as 

 the zoospores become ripe, a gentle oscillatory 

 motion is seen in the upper part of the spore- 

 case. This is accompanied with a compres- 

 sion of its contents, in consequence of which 

 its membrane gives way at its weakest point, 

 viz. the apex of the terminal conical projec- 



Fig. 135. 



Sporangium of Saprolegnia ferox, during the expul- 

 sion of the zoospores, 200 diam. 

 (All the figures, from 129 to 135 inclusive, are from 

 Thuret) 



tion. In its most perfect condition, the zo- 

 ospore of Saprolegnia consists of a pyriform, 

 protoplasmic, membraneless corpuscle, which 

 is furnished with a pair of cilia, emanating from 

 its apex. It is remarkable for the short dura- 

 tion of its motion, the cessation of which la 

 immediately followed by germination.* 



* For the history of the second period of the 

 vegetative life of Saprolegnia, see below, 19. 

 It is only under the most favourable conditions 

 that the zoospores of Saprolegnia assume the form 

 described in the text. Very frequently at the period 

 of their escape, they are sp'heroidal corpuscles unen- 

 dowed with the power of motion, if uot incapable of 

 germination. In this case, according to Anton de 

 Bary, the completion of their development takes 

 place outside of the spore-case. He describes the 

 accumulation of the escaped, but imperfectly formed, 

 zoospores in rounded heaps (Kopfchen), which re- 

 main for several hours in contact with the termina- 

 tions of the tubes from which they have escaped, 

 and finally become invested with a* cellulose-mem- 

 brane. Within this membrane their development 

 is completed ; and when they at last escape, they 



