THE PLANT 45 



which we may term " self -poisoning." This phenom- 

 enon shows itself in a general slowing of the growth- 

 rate, and in diminished reaction to external changes, 

 such as temperature; it is nearly akin to muscular 

 fatigue. Usually the oldest parts of the plant or, 

 rather, the terminal buds of each part are the first to 

 show it, and the main stem first of all (Figs. 4 and 10). 

 This cessation of growth of the main stem has an effect 

 on the flowering later on, for, since no more flowering 

 branches can be formed in an upward direction, flowering 

 must stop when all the existing flowering branches have 

 opened all their flowers, unless lateral vegetative branches 

 exist to take up the work. 



Like all other features of the plant, although this 

 senescence may be induced by ill-treatment at any time, 

 it is a specific reaction which varies with different kinds 

 and strains of cotton-plants. Under the same con- 

 ditions of cultivation some kinds show it at a very early 

 age in the terminal bud of the main stem, and are com- 

 mercial failures thereby; others show it so late that the 

 flowers they have formed are as many as can be ripened 

 off before the winter comes ; and others may not show it 

 at all, but continue year after year to respond directly to 

 |^i e limiting factors of the environment, and be known 

 as ''tree cottons" (PL II.). 



eover, senescence is not irremediable with cotton- 

 it is with mankind at present. A senescent bud 

 may recover after a prolonged rest, and probably we 

 shall be able to obtain such recovery almost instantly 

 when the nature of the poisons is known. The result of 



