CH. VIIl] MUCOK. Ill 



simple process. One example has been considered in 

 the case of yeast, where a young cell buds from the 

 parent and becomes a new plant. Here, and in similar 

 cases, growth cannot be distinguished from reproduction. 

 A cell gets bigger by means of growth, the process 

 becomes reproduction when the increment breaks loose 

 from the parent. This comparison does not by any 

 means make reproduction easier to understand, it merely 

 shows that in growth the mystery of reproduction is really 

 present. 



The green dust found on the trunks of trees is made up 

 of countless millions of the plant Pleurococcus : like yeast 

 it is a unicellular plant, but instead of being a unicellular 

 fungus it belongs to the great class of chlorophyll-con- 

 taining plants. It obtains its food from the air, and from the 

 water trickling down the tree. Its manner of nutrition 

 is like that of other green plants and need not be further 

 considered. Under the microscope it is seen to consist of 

 minute green cells, more or less massed together in 

 clusters, and presenting a number of different stages of 

 cell division. A single cell divides by a cross-wall into 

 two compartments, then into four, and then into eight. 

 Various intermediate stages are to be found, and it can 

 also be seen how the compartments, into which the parent 

 is divided, disintegrate into their component cells, which 

 finally fall apart. 



Mucor. 



For a study of specialised asexual reproductive cells 

 Mucor, one of the many fungi known as moulds, is 



