16 BULLETIN 1018, IT. S. DEPARTMENT OF AGRICULTURE. 



period of hibernation, at the commencement of which the growth and 

 fruiting activities gradually slow up and finally cease. Such be- 

 havior is considered entirely normal for the cotton plant, and it is 

 commonly thought to bear a definite relation to the seasonal fall in 

 temperature. A survey of the literature on the cause of such be- 

 havior reveals the presence of two widely diverse opinions, one of 

 which views the cessation of activity as a direct response to changing 

 external conditions and the other as the result of fixed, hereditary, 

 internal causes. In the West Indies, where the tendency of the Sea 

 Island cotton is toward perennial habits, the flowering curves as pre- 

 sented by Harland (14) show that a period of cessation in activity 

 occurs about 90 days after the appearance of the first flower. After 

 this, there is renewed activity and another distinct node is pro- 

 duced in the flowering curves. Balls (3) shows by growth and flower- 

 ing curves that in Egypt there are remarkable differences between 

 different strains of cotton grown under similar environmental condi- 

 tions in respect to the time when growth and flowering cease. In 

 discussing the phenomenon of cessation of activities he applies to it 

 the term " senescence " and ascribes it to self-poisoning. He postu- 

 lates that the influence is of a chemical nature, a thermotoxy local in 

 and peculiar to the growing point. 



From figures 1 and 3 it appears that in Arizona there may be 

 variations in periodicity in the same strain, planted at the same time, 

 grown in the same type of soil, and. with all other conditions similar 

 except soil-moisture content. This is noticeable during the later 

 development of the plants when the transition from full activity into 

 a condition, of hibernation is taking place. It will be observed that 

 until about August 20 the increase in growth per week was influenced 

 by a proportionate amount of moisture present in the soil. After this 

 date there was a more distinct slowing of the growth rate of plants 

 on plats 1 and 2 than on the other two plats. This occurred despite 

 the fact that the amount of soil moisture in plats 1 and 2 was greater 

 than in the other two plats. 



Balls (3) states that " when dealing with most pure strains, we 

 find considerable uniformity in the date of the first flower. The 

 stunted plants, if any, flower late, so that a close correlation here 

 exists between the height of the young stem and the flowering date." 

 However, in this connection he states that " all the plants of some 

 strains in the author's possession (notably King Upland) come into 

 flower almost simultaneously, even if some are stunted." In the 

 writer's experiment, while there was a difference in the average 

 height of the plants on the different plats at the time when flowering 

 began, about June 30, there was a decided uniformity in the time 

 the first flowers appeared. Though the average height of plants on 



