342 



Conjugate 



Wittr. (diarn. 4 /z) and M. minutissima Lemm. (diam. 2'5 3/u) ; the largest is the American 

 species M. crassa (Wolle) De Toni (diam. 50 p). 



The ' knee-joint ' connections of Mougeotia genuflexa (Dillw.) Ag. [ = M. miraUlis (A. Br.) 

 Wittr.] are deserving of special mention. In north temperate countries this is a common 

 species and although rarely seen in conjugation, contact regularly takes place between 

 neighbouring filaments by means of genuflexions of the cells. These 'knee-joints' of 

 contact have all the outward appearance of the commencement of scalariform conjugation, 

 but Nieuwland ('09 A) has brought forward evidence to show that this is not the case. 

 These contact cells appear to be simply glued together and no direct communication is 

 ever established between them. Nieuwland's observations indicated that filaments thus 

 connected very readily break up into their individual cells, and, since this results in an 



Fig. 218. A F, Debarya Hardyi G. S. West. A, conjugating filaments; B D, extremities of 

 gametangia during conjugation showing gradual filling up of internal cavity ; E and F, com- 

 pleted zygospores. G K, D. desmidioide.s W. & G. S. West. G and H, small portions of long 

 vegetative filaments; I, conjugating cells; J and K, completed zygospores. A, E and F, 

 x470; BD, x940; G K, x 488. 



immediate increase in the quantity of Mougeotia, presumably the dissociated cells divide 

 rapidly to form new filaments. Nieuwland regards this 'knee-joint' connection of the 

 filaments as 'a phenomenon preliminary to the process of vegetative multiplication.' The 

 physiological significance of the temporary connection may be an interchange of soluble 

 substances through the apposed walls of the joint, but the whole question requires detailed 

 investigation. 



In Mougeotia gracillima and M. parvula the chloroplast is occasionally constricted and 

 in several instances the present author has observed two chloroplasts in each cell, with the 

 nucleus located between them. This condition is a near approach to the cytological 

 structure of the Desmid Gonatozygon Kinahani, but the latter has characters which easily 

 distinguish it from any species of Mougeotia. 



