FORMS WITH CONNECTED FRUSTULES. 295 



after self-division, attached by a gelatinous cusMon, or by a 

 dichotomous stipes (Fig. 89). Many of these present a strong re- 

 semblance to some of the preceding, so far as the structure of 

 their frustules is itself concerned ; so that when, as frequently 

 happens, they are found unattached, the diflFerence is not appa- 

 rent. In Synedra (Fig. 102, l), which is not unlike a long nar- 

 row liJ'avicula (an imperfect longitudinal line, with central and 

 terminal dilatations, being often, but not always, apparent), the 

 frustules are at first invariably attached to larger Algse, or other 

 aquatic plants, by a cushion-like gelatinous basis ; and when they 

 remain adherent to this after repeated subdivision, they some- 

 times form a fan-like band of frustules, not unlike that of Lic- 

 mophora (Fig. 91), or even a stellate cluster, the appearance of 

 which is extremely characteristic. So again, the frustules of 

 Cromphonema (Fig. 90) in a side view, are not unlike those of 

 l^avicula; but they are distinguished in front view by their 

 cuneate (wedge-like) form, which arises chiefly from the une- 

 qual development of the membrane connecting the valves, at the 

 upper and lower ends. The stipes seems to be formed by an 

 exudation from the frustule, which is secreted only during the 

 process of self-division ; hence when this pi'ocess has been com- 

 pleted, the extension of the single filament below the frustule 

 ceases; but when it recom- 

 mences, a sort of joint or articu- Fio. 90. 

 lation is formed, from which a ^ ° " 

 new filament begins to sprout 

 for each of the half-frustules ; 

 and when these separate, they 

 carry apart the peduncles which 

 support them, as far as their ^'.'M f 



fIivero"finf»A pan tnkfi nlanp • and { -k'^i ' 



divergence can take place ; and 

 it is in this manner that the 

 dichotomous character is given 

 to the entire stipes (Fig. 89). 

 The species of Gomphonema 



are, with scarcely an exception, Gomplwnam gemmatum:—^, siae view of frus- 



inhabitauts of fresh water: and '"'^ """^'^ *"'=''''' "■^snifif^''; b, from view; c, 



,n , rt frustule 111 the act of self-division. 



are among the commonest forms 



of Diatomacese. In Licmophora (Fig. 91) we meet with a dif- 

 ferent mode of growth ; for the newly formed part of the stipes, 

 instead of itself becoming double with each act of self-division 

 of the frustule, increases in breadth, while the frustules them- 

 selves remain coherent ; so that a beautiful fan-like arrangement 

 is produced. A splitting away of a few frustules seems occasion- 

 ally to take place, from one side or the other, before the elonga- 

 tion of the stipes ; so that the entire plant presents us with a more 

 or less complete _^a6e& or fan upon the summit of the branches, 

 with imperfect flabellae or single frustules irregularly scattered 

 throughout the entire length of the footstalk. This beautiful 

 plant IS marine, and is parasitic upon sea-weeds and zoophytes. 



