i6 



MICROSCOPIC PLANTS. 



[CHAP. 



ing branches are given off, and we soon have a com- 

 plete colony of moulds. 



Another mould (Mucor mucedo) bears a consider- 

 able resemblance to the last, though the plant is not 

 divided into a number of cells, 

 but is one continuous cell. A 

 large round cell is formed at the 

 summit of an aerial hypha, the 

 protoplasm of which divides into 

 a number of smaller cells. These 

 are the spores, and the large cell 

 in which they are formed is called 

 the sporangia. The wall of the 

 sporangia bursts and scatters the 

 spores. 



An interesting thing about 

 many of these fungi is what is 

 termed polymorphism, or many 

 forms. Thus Torula is believed 

 by some scientific men to be merely a form of some 

 mould like Penicillium or Mucor, and that the differ- 

 ence in form depends upon the substance they are 

 growing on or in. Penicillium has been found to 

 give rise, under certain conditions, to another form 

 previously ranked as an independent species of Euro- 

 tium. In Puccinia graminis (fig. 18) and jEcidium 

 berberidis (fig. 19) there is a remarkable inter- 

 change of form, according to the. plant on which it 

 is parasitical. Puccinia is the "rust" which farmers 

 find so destructive to wheat, whilst jEcidium is a 

 parasite upon the Berberry. There is an old agri- 

 cultural belief that Berberry bushes near cornfields 



FIG. 17. 



