54 Growth 



others, they often display shapes by no means spherical. Many unicellular 

 green algae and the simpler fungi are examples of this. Von Hofsten and 

 von Hofsten (1958) have explored the effect of various factors on cell 

 shape and thus on vegetative characters in the ascomycete Ophiostoma. 

 In the development of cell shape genetic factors are doubtless impor- 

 tant, and these appear to control cytoplasmic patterns, wall differences, 

 and other factors. Cell shape is one aspect of the more general problem 

 of differentiation. 



Much of morphogenetic significance can be learned from a study of 

 individual cells. A knowledge of their relations to each other, and par- 

 ticularly of the way in which they form cell aggregates, is still more im- 

 portant. This involves the general problem of meristematic activity, the 

 subject of the next chapter. 



