246 



Siphonales 



up, asexual bodies of the nature of ' cysts ' or gemmae may be produced. 

 These cysts (sometimes rather misleadingly referred to as 'akinetes') 

 were well described and figured by Stahl (79), after they had been first 

 noticed by Ktitzing 1 . They are shortly cylindrical bodies with thick cell- 

 walls, and they may either germinate directly into a new filament or the 

 protoplasmic contents may escape from the old wall before germination 

 commences. Very often they break up into amoeboid bodies, which soon 

 round themselves off and become invested with a cell-wall, after which they 

 either rest for a time or grow directly into new filaments. In some instances, 

 due as a rule to unfavourable conditions of growth, septa appear at intervals, 

 breaking up the filaments into a number of thick-walled segments which are 

 also of the nature of rudimentary gemmaa or cysts. 



00 



Fig. 159. The sexual organs of Vauclieria. A and B, V. sessilis (Vauch.) DC. ; C and D, 

 V. hamata (Vauch.) Lyngb. E, oogoninm and oospore of V. ornithocephala Ag. A D, 

 x 200 ; E, x 320. a, antheridiurn ; an, antherozoid ; oo, oogoniuni. 



Dichotomosiphon produces curious tuber-like swellings at the extremities 

 of the branches which may be compared with akinetes (fig. 161 A and Bt). 

 These always grow directly into new plants. 



Sexual reproduction of a high type occurs in the Vaucheriacese, this 

 family standing alone amongst the Siphonales in the possession of sharply 

 differentiated oogonia and antheridia. The sexual organs are developed at 

 scattered intervals along the cylindrical filaments, and, except in the 



1 Kiitziug (Tub. Plnjc. iv, t. 98) figured this state of Vauclieria as ' Gonyrosira dichotoma,' an 

 unfortunate error which has given rise to much confusion, since it has, of course, no relationship 

 with the species of the true Gongrosira (a genus of the Ulotrichales). Consult G. S. West, '04, 

 p. Ill ; and Herring, '07, p. 116. Kiitzing recorded the fact that his ' Gongrosira ' grew into 

 tilaments of Vancheria. 



