1914J BAILEY & SINNOTT—PHYLOGENY OF ANGIOSPERMS 47 



annual ring, root, node, reproductive axis, or any other particular 

 region. However, the meristematic tissues of the developing plant 

 are in all probability more subject to modifying environmental 

 influences than are the embryos of the higher animals. It is 

 therefore not at all surprising that in many cases the normal con- 

 servatism of the embryonic tissues in any region should be more or 

 less neutralized by local physiological changes in the same way that 

 reversions to a more primitive type of structure may be recalled by 

 abnormal stimuli or by traumatism. Nor is it necessary to suppose 

 that all regions of the plant will be subject simultaneously to similar 

 modifying influences. In any given individual or group of individ- 

 uals, palingenetic characters may occur in one or more regions 

 when they have been lost or replaced by cenogenetic structures 

 in others. It may be seen, therefore, that very misleading conclu- 

 sions will undoubtedly be drawn by assuming that a given character 

 which appears in a certain conservative region of the plant is primi- 

 tive, unless reliable corroborative evidence exists. In determin- 

 ing the possible antiquity of a given character it is essential that 

 its structure, development, and behavior under different environ- 

 mental and nhvsioWical conditions should be studied and corn- 



living 



forms 



The results of such investigations are in general most con- 

 clusive when concerned with categories of characters which have 

 been termed " degradational " or " regressive,'' that is, characters 

 which are being reduced or lost. Jackson ('99), in his study of the 

 leaves of a number of gymnosperms and angiosperms, has con- 

 tributed much toward the elucidation of the behavior of these char- 

 acters. He has shown that in plants which are losing foliar 



sim 



stems 



stimulating types of injury. On the other hand, stunted, feeble, 

 senile conditions tend to hasten the process of reduction, just as 

 on stunted or sickly mature twigs or very old specimens, of a 

 species which has not suffered reduction; the leaves may undergo 

 an incomplete development and revert to the seedling type through 

 a failure in their individual ontogeny to develop full specific char- 



