CHARACE.E 



i8i 



usurp the functions of the primary root. The upper of the two nodes 



is still at some distance from the apex of the prothalHum, this apical 



portion above the upper node consisting of a few much shorter cells. 



From this upper node is developed the new 



plant. It is divided by longitudinal septa into 



two inner and six or eight peripheral cells. The 



peripheral cells ultimately become rudimentary 



leaves, which do not, however, form a true whorl. 



In the midst of them appears a bud, or growing 



point, developed from one of the inner cells, from 



which springs the new stem, in a direction nearly 



at right angles to that of the prothallium. At 



present the formation of the prothallium has been 



observed only in the genus Chara. 



A remarkable instance of parthenogenesis has 

 been recorded in Chara crinita (Wallr.). The 

 species is dioecious, and male plants are extremely 

 rare. On the female plants the oospheres develop 

 into oosperms without apparently any possibility of 

 their having been impregnated ; and the spermo- 

 carps thus formed germinate in the ordinary way. 



The Characeae consist of only a compara- 

 tively small number of species, but some of them 

 very abundant, growing submerged in deep or in 

 shallow, in stagnant or in running, or occasionally 

 in brackish water. Several species are grown with 

 great facility in fresh-water aquaria, where they 

 multiply very rapidly. The presence of certain 

 species may be detected by the fcetid odour of 

 sulphuretted hydrogen given off when decaying. 

 Phipson (Compt. Rend., Ixxxiv., 1879, pp. 316, 

 1078) attributes this odour to the presence of a 

 special substance which he calls characin. The 

 typical genus Chara is distinguished by its power 

 of extracting calcium carbonate from the water in 

 which it grows, the whole plant becoming thus 

 covered with a calcareous incrustation, which 

 frequently renders it difficult to make out the 

 structure. Hence the family has acquired the popular names of 'brittle- 

 worts' and 'stoneworts.' Nitella translucens (Ag.) sometimes forms 

 enormous mat-like masses at the bottom of ponds. 



The systematic position of the Characeas has been a matter of much 



Fig. 168. — Germination of C. 

 fragilis. sp, spermocarp ; 

 «'', first root ; i, first inter- 

 node of prothallium ; d, 

 first node ; iv" , rhizoids ; 

 q, second elongated inter- 

 node ot prothallium ; g, 

 second node with first whorl 

 of leaves ; j>l, apical por- 

 tion of prothallium (x 4). 

 (After Pringsheim.) 



