DIV. ii PHYSIOLOGY 303 



Every departure from this complex of causes will also find its ex- 

 pression in the form of the plant. 



Alterations of the normal form tend to be more extreme the 

 younger the cells are which are influenced. When the embryonic 

 substance of a growing point is diverted from its normal course of 

 development, a quite different structure may replace the one which 

 was anticipated ; in other cases intermediate forms of more or less 

 monstrous appearance are developed. The embryonic substance of a 

 growing point is still capable of giving rise to all the primordia which 

 are included in the range of form of the species, and thus a vegetative 

 shoot may arise in place of a leaf ; in exceptional cases even the 

 growing point pf a root may continue its development as a shoot. 

 On the other hand, the alteration of leaves that have commenced to 

 develop is mainly restricted within the limits of the metamorphosis of 

 the leaf ; thus, for example, petals may be formed in place of stamens 

 or carpels. The later the transforming influence takes effect on the 

 primordium, the more incomplete will be its transformation. 



All anomalous formations and functions of plants constitute the province of 

 PHYTOPATHOLOGY ( 62 ) ; pathological morphology is concerned with the former. 

 Monstrosities of external form are treated of under VEGETABLE TERATOLOGY ( 63 ) 

 and the pathological alterations of the shape and contents of cells and tissues in 

 the pathological anatomy of plants ( M ). 



The development of an organism does not proceed always with the 

 same activity or in continuous uniform growth. Usually periodic 

 alterations are evident, resting periods alternating with others of 

 active growth. During the latter, cell divisions periodically take 

 place, various forms of leaves and shoots arise, and reproductive organs 

 are developed ; periodically also larger and smaller parts of the 

 organism die off. 



A. Resting Condition and the Commencement of Growth ( 65 ) 



Attention has already been directed to the fact that three distinct 

 states may be recognised in the plant : active life, latent life, and 

 death. It was further pointed out that all the manifestations of life 

 are at a standstill in the condition of latent life ; the activities 

 of metabolism, even respiration, are suspended, and there are no 

 indications of growth and movement. The capacity of development 

 still remains, however, and this distinguishes latent life from death. 



Resting Condition. The condition of latent life is met with in 

 seeds, in the spores of some lower plants, and in many fully-grown 

 parts and buds of plants during unfavourable periods of the year (cold 

 periods, dry periods). It cannot be endured indefinitely by plants ; 

 even seeds and spores in which it is most complete lose sooner or later 

 the capacity of development and die. In other cases, as in the 



