CONJUGA T.-E 263 



In Gonatonema notabile (Wittr.) parthenogenetic hypnospores are formed 

 by tripartition of the contents of an ordinary cell which swells up into 

 the form of a cask. 



The phenomenon of reproduction in the Mesocarpaceae is regarded 

 by some as a rudimentary appearance of an 'alternation of generations.' 

 The sexual generation or oophyte is completed by the production of the 

 zygosperm as the immediate product of fecundation. This does not 

 germinate directly, but its- formation is immediately followed by cell- 

 division, or the development of the non-sexual generation or sporophyte ; 

 the sporocarp consists of the germinating hypnospore in the immediate 

 formation of which no process of impregnation took part and the in- 

 vesting sterile cells or ' pericarp.' Pringsheim, regarding the process of 

 conjugation in the Mesocarpaceas as representing a distinctly higher type 

 than that in the Zygnemaceae, divides the process in the former family 

 into two stages. The first stage, to which he applies the term ' copula- 

 tion,' consists in the simple union of two cells by the absorption of the 

 dividing cell-wall ; the second stage is an intimate coalescence of the 

 protoplasmic contents of the conjugating cells, effected by the motility of 

 the chlorophyll-bodies; and this stage he terms 'connubium.' The 

 hypnospore might, indeed, be correctly termed a ' carpospore,' and we 

 have here a point of departure in the direction of a much more highly 

 specialised type of structure. But the complete similarity of the two 

 conjugating cells before conjugation necessitates the retention of the 

 Mesocarpaceae among the Conjugatae. 



Limiting the order in accordance with the above-named characters, 

 the genera which the Mesocarpaceae comprise are Mesocarpus (Hass.), 

 Staurospermum (Ktz.), Craterospermum (Br.), and Gonatonema (Wittr.). 

 Several species of Mesocarpus and Staurospermum are not infrequent in 

 stagnant water, especially in moor pools and among Sphagnum. The 

 filaments are not so copiously invested with mucilage and not of so 

 bright green a hue as those of the Zygnemaceae ; Staurospermum 

 capucinum (Ktz.) has a beautiful violet tinge. 



LITERATURE. 



Wittrock Algologiska Studier, Upsala, 1867 ; Orn Gotlands och Oelands Sotwas- 

 seralger, 1872 (Quart. Journ. Micr. Sc., 1873, p. 123); On the Spore-formatioa 

 of the Mesocarpece, 1878. 



