CELL-MULTIPLICATION IN CONFERVA. 317 



then come to rest and sink to the bottom, where they remain 

 heaped in green masses. What is their future history, has not 

 yet been ascertained ; but there is evidence from analogy that 

 they are " antheridial" cells, which have for their office to fecun- 

 date the true germ-cells by contained antherozoids. No develop- 

 ment of "resting-spores," however, has yet been observed. The 

 rapidity of the growth of this curious plant, is not one of the 

 least remarkable parts of its history. The individual cells of 

 which the net is composed, at the time of their emersion as 

 gonidia, measure no more than l-2500th of an inch in length ; 

 but in the course of a few weeks, they grow to a length of from 

 l-12th to l-3d of an inch. 



198. Almost every pond and ditch contains some members of 

 the family Gonfervacece ; but they are especially abundant in 

 moving water ; and they constitute the greater part of those 

 green threads, which are to be seen attached to stones, with their 

 free ends floating in the direction of the current, in every run- 

 ning stream, and upon almost every part of the sea-shore, and 

 which are commonly known under the name of " silk-weeds" or 

 "crow-silk." Their form is usually very regular; for each 

 thread is a long cylinder, made up by the union of a single file 

 of short cylindrical cells united to each other by their flattened 

 extremities ; sometimes these threads give off lateral branches, 

 which have the same structure. The endochi'ome, though 

 usually green, is occasionally of a brown or purple hue ; it is 

 sometimes distributed uniformly throughout the cell (as in Fig. 

 107), whilst in other instances it is arranged in a pattern of some 

 kind, as a network or a spiral ; but this may be only a transi- 

 tional stage in its development. The plants of this order are 

 extremely favorable subjects for the study of the method of cell- 

 multiplication by binaiy subdivision. This process usually takes 

 place only in the terminal cell; and it may be almost always 

 observed there, in some one of its stages. The first step is seen 

 to be the subdivision of the endochrome, and the infiection of 

 the primordial utricle around it (Fig. 107, a, a) ; and thus there 

 is gradually formed a sort of hour-glass contraction across the 

 cavity of the parent cell, by which it is divided into two equal 

 halves (b). The two surfaces of the infolded utricle produce a 

 double layer of cellulose membrane between them ; this is not 

 confined, however, to the contiguous surfaces of the young cell, 

 but takes place over the whole exterior of the primordial utricle, 

 so that the new septum is continuous with new layers that are 

 formed throughout the interior of the cellulose wall of the original 

 cell (c). Sometimes, however, as in Conferva glomerata (a common 

 species), new cells may originate as branches from any part of the 

 surface, by a process of budding; which, notwithstanding its 

 difference of mode, agrees with that just described in its essential 

 character, being the result of the subdivision of the original cell. 

 A certain portion of the primordial utricle seems to undergo 



