SIMPLE PLANTS 



205 



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.) 



Fig. 95. 

 The Union of the Gametes in Spirogyra. 



A, two filaments of Spirogyra qiiinina, 

 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.) 



becoming smaller as a thick- 

 ened 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 preparatory process 

 to permit a mixing of the par- 

 ent chromatin before actual re- 

 production 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 conjugating and fusing 

 parent cells are known as 

 gametes.* 



The spore cannot escape 

 from the parent cell, however, 

 until such parent-cell decays. 



Artificial Fertilization. 

 "More than a hundred years 



Fig. 96. A Common Foliose Lichen (Parmelia) 



Growing Upon a Board, and Snowing 



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). 



