GENERATIVE PROCESS IX DIATOMACEvE. 



285. 



Protophytes, and with the fact that the Sporangial frustules un- 

 doubtedly thus multiply by gonidia (§ 219), seem to justify the 

 conclusion that such a method of multiplication does obtain in 

 this group. And it is not at all improbable that very considerable 

 differences in the size, form, and markings of the frustules, such 

 as many consider sufficient to establish a diversity of species, have 

 their origin in this mode of propagation. It is probable that, so 

 long as the vegetating processes are in full activity, multiplicatiou 

 takes-place in preference by self -division ; and that it is when 



Fig. 122. 



Conjugation of Epitkemia turgida: — a, front view of single 

 frustule ; b, side view of the same ; c, two frustules with their 

 concave surfaces in close apposition ; d, front view of one of the 

 frustules, showing the separation of its valves along the suture ; 

 e, f, side and front views after the formation of the sporangia. 



deficiency of warmth, of moisture, or of some ether condition, 

 gives a check to these, that the formation of encysted Gonidia, 

 having a greater power of resisting unfavourable influences, will 

 take-place ; whereby the species is maintained in a dormant state 

 until the external conditions favour a renewal of active vegeta- 

 tion (§ 192). 



219. The process of Conjugation or true Generation has been 

 observed to take-place among the ordinary Diatomaceaa, almost 



