130 PRINGSHEIM, ON THE IMPREGNATION 



affords zoospores, which escape from the cells forming the 

 joints ; but of this also he does not appear to have any certain 

 proof. He describes antheridia, precisely like those of Spha- 

 celaria and developed in the same way, in the terminal cells 

 of the lateral ramules in the closely-allied Cladostephus 

 spongiosus. 



With respect to the fresh-water Algae most nearly allied to 

 Vaucheria, it is, perhaps, sufficiently clear from the author's 

 observations on that species, that these plants, besides the 

 asexual, gemmate multiplication by zoospores, also present 

 a true sexual propagation. The most probable supposition 

 would be that the female organs of these plants, as in 

 Vaucheria are to be sought in the quiescent-spores, which have 

 been found in many genera. But in the next place it remains, 

 not only to discover the antheridia in these plants, but also to 

 show the possibility of the entrance of the spermatozoids into 

 the interior of the quiescent spores, through an opening in the 

 spore-memhrane ; or as in the FucacecB the impregnation of the 

 sporules externally to the parent body. 



The author's observations on these points, though incom- 

 plete, may still be serviceable towards further research. 



The asexual multiplication of Acldga prolifera is well 

 known, but besides the zoospores this plant also presents 

 quiescent spores contained in peculiarly shaped sporangia. 



The author finds that these spores germinate in the same 

 way as do those of Vaucheria. He found also that before the 

 formation of the quiescent spores, and in some measure 

 simultaneously with the division of the contents into the 

 masses destined to become quiescent spores, a great many 

 minute, oval, sharply-defined openings are formed by the 

 absorption of the cell-wall of the sporangium in several places, 

 which constitute so many open passages into the interior of 

 the sporangium even whilst its contents are in progress of 

 formation into quiescent spores. The object of these openings 

 is clearly to allow of the entrance of the spermatozoids into 

 the dividing spore-mass. In this case, also, the action of the 

 spermatozoids must be exerted upon the contents of the 

 sporangium ivhilst undergoing division and not upon perfectly- 

 formed spores, for, long after the openings have been formed, 

 the segments of contents of the sporangium, are not even 

 separated, and far less do they represent fully-formed cells. 



This process of development indicates a great similarity 

 between Vaucheria and Acldya ; but whilst in the summit of 

 the tube in Vaucheria a single large zoospore is formed, in 

 that of Achlya very many smaller zoospores are produced, and 

 the same is the case with respect to the quiescent spores ; 



