

540 MICROSCOPIC FORMS OF VEGETABLE LIFE THALLOPHYTES 



110 disposition to separate from each other spontaneously. Still 

 they correspond with those which are strictly unicellular, as to the 

 absence of differentiation, either in structure or in function, between 

 their component cells, each one of these being a repetition of the 

 rest, and no relation of mutual dependence existing among them ; 

 and all such simple organisms, therefore, may still be included 

 under the general term of Thallophytes. 



Excluding lichens, for the reasons to be stated hereafter, botanists 

 now rank these thallophytes under two series : algce, which form 

 chlorophyll, and can support themselves upon air, water, and mineral 

 matters; and fungi, which, not forming chlorophyll for themselves, 

 depend for their nutriment upon materials drawn from other organ- 

 isms. Each series contains a very large variety of forms, which, 

 when traced from below upwards, present gradually increasing com- 

 plexities of structure ; 

 and these gradations 

 show themselves espe- 

 cially in the provisions 

 made for the genera- 

 tive process. Thus, in 

 some forms, a 'zygo- 

 spore ' is produced by 

 the fusion of the con- 

 tents of two cells, 

 which neither present 

 any apparent sexual 

 difference the one 

 from the other, nor 

 can be distinguished 

 in any way from the 

 rest. In the next 

 highest forms, while 

 the 'conjugating' cells 

 are still apparently 

 undifferentiated from 

 the rest of the structure, a sexual difference shows itself between 

 them ; the contents of one cell (male) passing over into the cavity 

 of the other (female), within which the 'zygospore' is formed. 

 The next stage in the ascent is the resolution of the contents 

 of the male cell into motile bodies (' antherozoids '), which, escaping 

 from it, move freely through the water, and find their way to 

 the female cell, whose contents, fertilised by coalescence with the 

 material they bring, form an ' oospore.' In the lower forms of this 

 stage, again, the generative cells are not distinguishable from the 

 rest until the contents begin to show their characteristically sexual 

 aspect; but in the higher they are developed in special organs, 

 constituting a true ' fructification.' This must, however, be dis- 

 tinguished from organs which, though commonly spoken of as the 

 * fructification,' have no real analogy with the generative apparatus 

 of flowering plants, their function being merely to give origin to 



I *^1 



FIG. 416. Continuity of protoplasm. (From Vines's 

 ' Physiology of Plants.' Cambridge University Press.) 



