330 HYDRODICTYON. FAMILY CONFERVACE.E. 



gelatinous envelope, and speedily increases so much in size as to 

 rupture the containing cell-wall, on escaping from which it presents 

 all the essential characters of a young Hydrodictyon. Thus, 

 whilst this plant multiplies itself by Macro-gonidia during the 

 period of its most active vegetation, this method of multiplication 

 by Micro-gonidia appears destined to secure its perpetuation under 

 conditions that would be fatal to it in its perfect form. The 

 rapidity of the growth of this curious organism 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 Gronidia, 

 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-3rd of an inch. — Nothing has been as yet ascertained respecting 

 the Sexual Generation of this type ; and the search for this is an 

 object worthy of the pursuit of any Microscopist who may possess 

 the requisite opportunities. 



249. Almost every pond and ditch contains some members of 

 the Family Confervacece ; 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 running 

 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, each thread being a long 

 cylinder made-up by the union of a single file of short cylindrical 

 cells united to each other by their flattened extremities : some- 

 times these threads give-off lateral branches, which have the same 

 structure. The Endochrome, though usually green, is occasionally 

 of a brown or purple hue ; it is sometimes distributed uniformly 

 throughout the cell (as in Fig. 153), 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 transitional stage in its development. The 

 Plants of this order are extremely favourable subjects for the study 

 of the method of Cell-multiplication by binary 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 

 inflexion of the Primordial Utricle around it (Fig. 153, 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 extends over the whole exterior of the primordial utricle, so 

 that the new septum becomes continuous with a new layer that is 

 formed throughout the interior of the cellulose wall of the original 

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

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



