STRUCTURE OF PALMOGLCEA 



541 



gonidial l cells or groups of cells, which simply multiply the parent 

 stock, in the same manner that many flowering plants (such as the 

 potato) can be propagated by the artificial separation of their leaf- 

 buds. It frequently happens among cryptogams that this gonidial 

 fructification is by far the more conspicuous, the sexual fructifica- 

 tion being often so obscure that it cannot be detected without 

 great difficulty ; and we shall presently see that there are some 

 thallophytes in which the production of govids seems to go on 

 indefinitely, no form of sexual generation having been detected 

 in them. These general statements will now be illustrated by 

 sketches of the life-history of some of those humble thallophytes 

 which present the phenomena qf cell-division, conjugation, and 



FIG. 417. Development of Palmoglcea macrococca. 



gonidial multiplication, under their simplest and most instructive 

 aspect. 



The first of these lowly forms of life to which we call the 

 attention of the reader is Palmogloea macrococca, Ktz., 2 one of 

 those humble kinds of vegetation which spread themselves as green 

 slime over damp stones, walls, &c. When this slime is examined 

 with the microscope, it is found to consist of a multitude of green 

 cells (fig. 417, A), each surrounded by a gelatinous envelope ; the cell, 

 which does not seem to have any distinct membranous wall, is filled 

 with a granular ' endochrome,' consisting of green particles diffused 

 through colourless protoplasm ; and in the midst of this a nucleus 



1 The term gonids, originally applied to certain green cells in the lichen-crusts 

 that are capable, when detached, of reproducing the vegetable portion of the plant, 

 is used by some writers as a designation of the non-sexual spores of cryptogams 

 generally, which it is very important to discriminate from the genitative ' oospheres.' 

 If possessed of motile powers, they are spoken of as : zoospores,' or sometimes (011 

 account of the appearance they present when a number are set free at once) as 

 1 swarm-spores.' In contradistinction to ' motile ' gonids or ' zoospores,' those which 

 show no movement are often termed resting spores, or hypnospores ; but such may 

 be either sexual oi'>S2)lieres or non-sexual 'gonids, the latter, like the former, often 

 ' encysting ' themselves in a firm envelope, and then remaining dormant for long periods 

 of time. 



- [Most of the species 'of Kiitzing's genus Palmoglcea are now regarded as belong- 

 ing to the Desmldiacece, and are included under the genus Mesotceninni. ED.] 



