108 ZYGOPHYCE.E. 



Wittrock includes his single genus Gonatonema in the Mesoearpets as 

 an agamosporous form, without ascertained conjugation. As an excuse 

 for this he says: "If we attached importance only to the neutral or 

 sexual nature of the spore formation, as some of the modern systema- 

 tizing botanists do even in the lower GryptogaMiCB, we should be obliged 

 to form a separate family for it, which might not even be placed in the 

 class of Conjugates. To me the accordance with Mesocarpece as to 

 the vegetative cells and the formation of the spores seems too great to 

 allow the separation of Gonatonema from this family. It may not be 

 unnecessary here to call to mind that the class of Diatomacecs in which 

 the formation of spores is in general effected through conjugation, does 

 also embrace some genera where the spores are formed neutrally." 



At the risk of condemnation as a " modern systematizing botanist," we 

 do not feel content to include this genus in the Mesocarpea, and have 

 therefore relegated it to a separate family until more complete evidence 

 is furnished as to whether it really should be associated with the Conju- 

 gate at all, although its affinities seem to lie in that direction. All we 

 are justified by the facts to assume is that it is an aberrant form, which, 

 on the faith of its vegetative character may for the present be retained 

 in proximity to the Mesocarpea? until its relationship is better established. 



GENUS 51. GONATONEMA. Wittrock. (1878.) 

 Spores (agamospores not carpospores) without conjugation, 

 formed by biseptation of the mother cells, which latter are bent 

 angularly, and alternately, at the point of fructification. 



Wittrock illustrates this genus by means of a species not yet ascer- 

 tained to be British, but which he regards as congeneric with Hassall's 

 species hereafter described. "Its vegetative stage consists of cylindric 

 cells arranged in a single row. The membrane of the cells is very thin, 

 and consists of pure cellulose. The bottoms of somewhat older cells 

 are gently curved inwards, which gives rise to a small lens-shaped room 

 between the cells. The contents of the cells consist of (1) a parietal 

 thin colourless layer of protoplasm ; (2) an axile cholrophyll-coloured 

 rather thick bard of protoplasm (the single chlorophyllaceous body of 

 the cell) which runs through the whole length of the cell, and which is 

 most frequently more or less excavated at both ends of the cell ; in the 

 band of chlorophyll occur the so-called ' starch granules,' in a number 

 of 2 to 4 ; (3) a rounded nucleus, which has its place at the side of the 

 chlorophyllaceons body, or very often in a small circular opening in the 

 middle part of the band of chlorophyll ; (4) small drops of oil, attached 

 partly to the inner side of the parietal layer of protoplasm, and partly 

 to the outer side of the chlorophyllaceous band ; and (5) colourless cell 

 liquid, which fills the vacuoles between the parietal layer of protoplasm 

 and the axile chlorophyllaceous band. 



" In purely vegetative cells the chlorophyllaceous body is found to pos- 

 sess the power of making free, and rather quick movements. This species 

 thus gives a second instance of independent movements of chlorophyl- 

 laceous bodies belonging to vegetative cells. 



" The formation of vegetative cells takes place by bipartition, exactly 

 in the same manner as in the llesocarpece. The cells destined to bring 

 forth spores have always a very considerable development as to length. 

 While the vegetative cells just formed by bipartition are only 5 to 6 

 times as long as thick, the cells which are ready to form spores are at 

 least 9, and more often 12 to 16 times as long as thick. A rather con- 

 siderable increase as to volume, by development in length, does conse- 

 quently take place in these cells before they are capable of fulfilling 

 their propagative purpose. 



