48 BOTANICAL GAZETTE [july 



acters. The suppression of characters may progress in two ways. 

 In most cases, the young plant, although more conservative in 

 acquiring new foliar characters, is more retentive of these char- 

 acters, once they become firmly fixed, than are most regions of the 

 mature stem. On the other hand, marked changes in the environ- 

 ment or physiological activity of the young plant may more or 

 less neutralize the effects of its natural conservatism. Under such 

 conditions the seedling may develop cenogenetic characters or lose 

 structures which are retained in mature portions of the plant. Thus 

 Jackson and Cope have shown that animals and plants may lose 

 ancestral characters by " retardation of development. That is, 

 features may appear at later and later stages in development until 

 they finally disappear/' 



Internal structures appear in general to behave in regression 

 and progression much as do external foliar characters. That 

 vigorous or stimulated types of growth tend to recall characters 

 which have been reduced has been illustrated, for example, by the 

 recurrence in such types of tissue of marginal tracheids in the Cu- 

 presseae, of resin canals in the Taxodieae, and of wood paren- 

 chyma in the later Araucarieae. It also seems to be true that the 

 influence of vigor and stimulating injuries in recalling reduced char- 

 acters are most effective in regions which are supposed to be con- 

 servative, such as the first annual ring, root, node, and reproductive 

 axis. 



In the Fagales there is apparently a very complete series of 

 species in which the successive stages of the reduction of wide 

 multiseriate rays can be traced in detail. This process of reduction 

 has taken place in most species by "retardation of development," 



the 



wide sheets of ray parenchvma. Unusuallv stimulatin 



hich 



cambium to form less com 



plete stages of the disintegration process. These stimul 



most 



be conservative, such as the first annual ring of roots and shoots, 

 the seedling stem, and node. In the process of reduction the tissue - 



- 



the pedu 



