150 



THE VARIOUS FORMS OF PLANTS 



spores have been formed by the division of the protoplasm mak- 

 ing up the ball or sporangium into many separate bodies. 



This method of the production of spores is evidently asexual. 

 These spores, if grown imder favorable conditions, will produce 

 more mycelia, which in turn bear sporangia. It has been found, 

 however, that at some time during the life of the mold another 

 method of reproduction is likely to occur. 



Formation of Zygospores. — Two hyphse which are close-lying 

 put out threads which communicate. The end of each of the 



threads cuts off a cell, and the two 

 cells, each from a different hypha, flow 

 together and mingle. In this condi- 

 tion they remain as a single resting 

 cell. This cell, which puts a heavy 

 I D wall around itself, is a zygospore. 

 Here again we have a process of con- 

 jugation similar to that we observed 

 in the pond scum. The ultimate re- 

 sult of the conjugation of the two cells 

 is that a new plant grows from the 

 zygospore after a period of rest. Dur- 

 ing the resting stage the spore may 

 undergo very unfavorable conditions, 

 even to extreme dryness, heat, or cold. 

 Conjugation of black mold : A, The use of the Zygospore to the plant 

 B, C, D, successive stages in jg evidently to Continue the species 

 the formation of the zygospore, ^^^j^^ ^^ unfavorable time in the life 



history of the plant. The process of conjugation is probably 

 a sexual process, as we have called it in pond scum. 



Physiology of the Growth of Mold. — Mold, in order to grow 

 rapidly, evidently needs oxygen, moisture, and heat. It obtains 

 its food from the material on which it lives. This it is able to 

 do by means of digestive ferments which are given out by the 

 rhizoids or rootlike parts of the hyphae, by means of which the 

 mold clings to the bread. These ferments change the starch of 



' It seems to have been proved recently that zygospores are formed by the union 

 of two cells, from different filaments, one of which has male, the other female, char- 

 acters. 



