206 



General Biology 



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Fig. 94. Chlorophycae, Rhodophycae, and Myxophycae. 



A. Cladophora, a branching green alga, a very 

 small part of the plant being shown. The branches 

 arise at the upper ends of cells, and the cells are 

 ccenocytic. 



B. A red alga (Gigartina), showing branching 

 habit, and "fruit bodies." 



C. Three common slime moulds (Myxomycetes) 

 on decaying wood: To the left above, groups of the 

 sessile sporangia of Trichia; to the right above, a 

 group of the stalked sporangia of Stemonitis, with 

 remnant of old Plasmodium at base; below, groups of 

 sporangia of Hemiarcyria, with a Plasmodium mass 

 at upper left hand. (A, after Caldwell; B, after 

 Schenck; C, after Goldberger.) 



The Union of the Gametes in Spirogyra. 

 A, two filaments of Spirogyra quinina, 

 side by side, showing stages in the union of 

 the cells (gametes) to form the zygospores; 

 B, another species (S. longata), in which the 

 cell unions occur between adjacent gametes in 

 the same filament. (After Schenck.) 



smaller as a thickened wall is 

 secreted about it. When this 

 latter event takes place, the 

 organism is said to be in a 

 spore state, and because the 

 spore has been formed by the 

 fusion of two cells, it is often 

 called a zygospore ( ). 



Conjugation is thus a prepara- 

 tory process to permit a mix- 

 ing of the parent chromatin 

 before actual reproduction 

 takes place. 



It has already been ex- 

 plained that a sexual germ-cell 

 is known as a gamete. The 

 zygospore is, therefore, now 

 one cell, the product of the 

 fusion of two gametes. There 

 is here, then, the beginning of 

 sex-life in the plant-world. 

 This is why the two conju- 

 gating and fusing parent cells 

 are known as gametes. 1 



The spore cannot escape 

 from the parent cell, however, 

 until such parent-cell decays. 



Artificial Fertilization. — 

 Something like a hundred years 



Fig. 96. A Common Foliose Lichen (Parmelia) 



Growing Upon a Board, and Showing 



Apothecia. (After Goldberger.) 



'This is the first sign of two sexes we shall see in the laboratory, although the very first sexual 

 differentiation in plants probably lies in the Volvacales (Fig. 97). 



