l60 SAPROPHYTIC FUNGI 



higher plant (p. 107) Every now and then the grow- 

 ing hypha branches, i.e. a new branch of the tube is 

 pushed out not far from the tip, and a new growing 

 hypha is thus produced. This continuous indefinite 

 growth and branching of the plant body is very 

 characteristic of typical plants as opposed to the 

 limtied compact growth of the typical animal (see 

 Chapter I, p. 22). From what is known in the case of 

 other fungi the growing tips of the hyphse are 

 probably sensitive to the stimuli of food substances 

 and of free oxygen, i.e. they wiU turn and grow 

 towards regions whence these substances are diffusing 

 towards the hypha. 



Reproduction. — (i) Spore formation. In place of 

 the simple cell division ot Amoeba, Protococcus and 

 bacteria, and the simple budding of yeast, the main 

 method by which Mucor multipUes and produces 

 new individuals is the formation of spores, produced 

 in special chambers (sporangia) cut off from the general 

 mycelium. Special hyphse (sporangiophores) arise as 

 branches of the mycehum and typically grow straight 

 up into the air. These sporangiophores are positively 

 phototropic, i.e. they grow towards brighter illumi- 

 nation. This generally involves growing away from 

 the substratum, so that the sporangium formed at the 

 end of the sporangiophore is placed in the best position 

 for free distribution of its spores into the air. 



The sporangium itself is formed by the swelling up 

 of the tip of the hypha (Fig. 16, a), so that under a 

 hand lens the sporangiophore looks like a minute pin 

 with a globular head (the sporangium). A cross wall 

 is formed, cutting off the head from the sporangiophore, 

 and the protoplasm of the sporangium breaks up into 

 a^pTfmber of tiny multinucleate cells, each of \yhicb 



