62 



MANUAL OF BOTANY 



Fig. 810. 



ColeochcBte is a form which in some respects approaches the 

 red seaweeds. Its thallus is composed of much-branched 

 filaments forming a tufted mass which grows apically or mar- 

 ginally. The cells in some cases bear peculiar sheathing hairs. 

 The plant bears antheridia and oogonia, each of the latter bearing 

 a trichogyne except in a few species. The antherozoid enters 

 the oogonium by an opening in the trichogyne and fertilises the 

 oosphere. 



The result of the fusion is the production of a more elabo- 

 rate sporophyte than in any other member of the Chloro- 



phycete. The oosphere se- 

 cretes a cell-wall round it, and 

 the oogonium in which it lies 

 becomes surrounded by a kind 

 of cellular covering derived 

 from the cells of the thallus 

 near it. It thus forms a kind 

 of fructification which becomes 

 detached from the parent. 

 Later the oospore germinates, 

 rupturing its coating ; it only 

 produces a few cells, each of 

 which gives rise to a single 

 zoospore. 



The asexual reproductive 

 cells produced by the Confer- 

 voideae are zoogonidia or zoo- 

 spores, as thej^ are produced 

 on the gametophyte or the 

 sporophyte respectively. They 

 are variously ciliated, and 

 always on germination pro- 

 duce a gametophyte [fig. 809). 

 The process of asexual reproduction is not found in the Desmids 

 nor in the Zygnemise. 



The last type of structure is found in the Charace^e, repre- 

 sented most familiarly by the two genera CJiara and Nitella. 

 In some respects these approach nearest in structure to the 

 liryophytes ; among the Chlorophyceae they are distinguished 

 by their relatively great degree of both morphological and 

 anatomical differentiation and by the complex structure of 

 their reproductive organs. 



Chara exhibits a long slender stem, bearing whorls of leaves 



Fig. 810. Longitudinal section tlirougli 

 the apical region of three primary 

 shoots of Chara fragilis. t. Apical cell, 

 in which segments are formed by 

 septa, each segment Ijeiug fnrtlier 

 divided by a curveil septum into a 

 lower cell not further divisible, which 

 develops into an internode, g, g', g", g'", 

 and an upper cell which produces a 

 node, m, m', and the leaves, &, h', h", h'', 

 which also undergo segmentation. 

 After Sachs. 



