294 BOTANICAL GAZETTE [may 



One or two ventral canal cells always persist without disorganizing, 

 which may also prevent the entrance of sperms and check the act of 

 fertilization. 



In Marsilia vestita, the species worked by Nathansohn, Stras- 

 burger tried Nathansohn' s method of inducing parthenogenetic 

 growth, but did not obtain a single parthenogenetic embryo. In this 

 species the sporophytic number 32 is reduced to 16 in sporogenesis, 

 and hence under natural conditions an embryo should develop only 

 after fertilization. He found similar normal conditions in M. quad- 

 rifolia, M. data, and M. hirsuta, whose chromosome number is the 

 same as that of M. vestita. 



According to his detailed account of sporogenesis in Marsilia 

 Drummondii, the number of megaspore mother cells is less than 16, 

 the usual number in normal forms, and sometimes only four. In 

 diakinesis 32 chromosomes appear, and in the metaphase there 

 were observed two kinds of mitotic figure?, one of heterotypic 

 type with 16 bivalent chromosomes, and the other of vegetative type 

 with 32 univalent chromosomes. In both cases a second division 

 follows, so that two kinds of megaspore tetrads are formed, one with 

 the 2.v or diploid number of chromosomes, and the other with the x 

 or haploid number. The proportion of these two kinds of spores 

 differs in each individual form; for instance, in Goebel's material 

 he found the megaspores with the diploid number only. In micro- 

 sporogenesis there was observed a tendency toward forming a hetero- 

 typic figure, but no mature sperms developed ; two species, M. macro, 

 and M. Nardu, behaved similarly. 



Such a megaspore forms a prothallium whose nuclei have the 

 diploid number of chromosomes, which pass to the egg nuclei, so 

 that the sporophytic number of chromosomes is maintained through- 

 out the life-history, as in cases of parthenogenesis known among seed 

 plants; however, the case found in Marsilia Drummondii by Stras- 

 burger, where a tetrad division occurs not accompanied by chromo- 

 some reduction, seems to be a condition never described before, 

 because most of the cases of parthenogenesis known in seed plants 

 are characterized by the omission of the tetrad division as well as the 

 accompanying reduction. 



Strasburger calls the phenomenon in Marsilia apogamy, main- 



