338 Conjugate 



protoplasmic mass)' in the conjugation -tube had been accomplished, the zygospore then 

 became divided by two or four septa into three or five cells, of which the central one was a 

 hypnospore, 'rich in chlorophyllaceous protoplasm (and later in oil), whilst the two or 

 four lateral cells, containing no chlorophyllaceous protoplasm are sterile and soon going to 

 die.' According to De Bary, therefore, the Mesocarpese have spores of two kinds, zygospores 

 which are formed by the growing together of the conjugating cells, without contraction, 

 and which do not repose, and hypnospores which are formed by the partition of the 

 zygospore and which rest for a time before germinating. 



Wittrock ('72; 78), after a most careful study of the conjugation in the Mesocarpeoe, 

 agreed with De Bary that the hypnospores could not be regarded as zygospores, but at the 

 same time he did not agree that the H-shaped 'double cells 'formed immediately on con- 

 jugation could be regarded as zygospores. He followed Pringsheim ('77) in considering the 

 H-shaped structure as a 'connubium,' the final result of conjugation being the formation 

 of several cells of which only the central one is fertile. He agreed with Pringsheim that 

 it was a sporocarp, with only one carpospore, and of a simpler type than occurs in any 

 other Algse. 



The actual facts of conjugation as detailed by Wittrock in the various 

 types of the genus Mougeotia are quite correct, but in the light of more recent 

 and exact knowledge of conjugation in the Zygnemacea3 as a whole, and 

 especially in view of the conjugation of Pyxispora, it is perhaps more correct 

 to regard the conjugation in the Mesocarpese as a fusion of a pair of isogametes, 

 the gametes themselves being derived from only a part of the protoplast of 

 the gametangium. The fertile spore the 'carpospore' of Wittrock may 

 therefore be regarded as a zygospore, since we know that its nucleus results 

 from a fusion of the nuclei of the gametes. 



Conjugation in Mougeotia is strictly isogamous except in M. tennis (Cleve) 

 Wittr. (= Plagiospermum tenue Cleve) where there is a slight sexual difference, 

 the zygospore being lodged very largely in one of the conjugating cells, which 

 might be regarded as the female gametangium. Such a type of conjugation 

 sometimes occurs in M. calcarea Wittr. ("72), a species in which are found all 

 the types of conjugation formerly used in discriminating between the ' genera ' 

 Mougeotia, Staurospermum and Plagiospermum. Other slight indications of 

 sexual differences are sometimes seen in the thicker conjugation-tubes of 

 some cells and in the location of the zygospore nearer to one gametangium. 



The usual type of conjugation in Mougeotia is scalariform ; that is, between 

 the cells of distinct filaments. Lateral conjugation between adjacent cells of 

 the same filament is only known to occur in one species of the genus, viz. 

 M. genuflexa (Dillw.) Ag. 



Parthenospores are sometimes formed, usually in isolated filaments which 

 have had no opportunity of conjugating, although in most cases among others 

 which have conjugated. The cells send out protuberances as if going to take 

 part in the formation of a conjugation-canal, and most of the protoplast, 

 including the chloroplast, moves into the protuberance, after which a wall 

 appears cutting it off as a parthenospore. Occasionally the parthenospore 



