SECTION 17.] 



TTTAIJ.OPTIYTFS. 



171 



set free is ready to germinate. Fig. 565 represents several stapes of the 

 Conjugating process, which, however, would never he found all together like 

 this in one pair of threads. 



513. Desinids and Diatomes, which are microscopic one-celled plants of 

 the same class, conjugate in the same way. as is shown in a Closterium by 

 Fig. 566, 567- Here the whole living contents of two individuals are in- 

 corporated into one spore, for a fresh start. A reproduction which costs 

 the life of two individuals to make a single new inn- would be fatal to the 

 species if there were not a provision for multiplication by the prompt divi- 

 sion of the new-formed individual into two, and these again into two, and 

 so on in geometrical ratio. And the costly process would be meaningless 

 if there were not some real advantage in such a fresh start, that is, in 

 sexes. 



514. There arc other Alga? of the grass-green series which consist of 

 single cells, but which by continued growth form plants of considerable 

 size. Three kinds of these are represented in Fig. 568-574. 



515. Lichens, Latin Lichenes, are to be studied in the works of the 

 late Professor Tnckerman, hut a popular exposition is greatly needed. 

 The subjoined illustrations (Fig. 575-580) may simply indicate what some 

 of the commoner forms are like. The cup, or shield-shaped spot, or knob, 

 which bears the fructification is named the Apothecium. This is mainly 



Fie.. 568. Early sta^c of a species of Hotrydium, a globose cell. 669, 570 

 of growth. 571. Pull- grown plant, extended and ramified below in i root-like 

 way. :">7"J A Vaucheria; single cell grown on Into a much-branched thread; the 

 eml of some brandies enlarging, and the green contents In one (a) there condensed 

 into :i spore. 573. More magnified riew <>f <i, and the mature spore escaping. 

 574. Bryopsis plumosa; apex of a stem with Its branehleta; all the extension of 

 one cell. Variously magnified. 



