THE ABORTION OF FRUITING BRANCHES IN COTTON. 15 



should not be ascribed to overshading alone. There is another form 

 of abortion of the fruiting branches that begins to show itself even 

 before the vegetative branches are large enough to keep the fruiting 

 branches from receiving their full share of sunlight. 



This physiological abortion of fruiting branches was observed at 

 Bard, Cab, in May, 1912, in Egyptian cotton thai had made normal 

 growth during a rather cool spring, but which was beginning to show 

 the effects of higher temperatures. As long as the weather continued 

 cool the vegetative branches remained small and the plants were be- 

 ginning to put forth fruiting branches when the warm weather began. 

 The effects of the heat were soon apparent in an accelerated develop- 

 ment of the vegetative branches, but the prosperity was not shared 

 by the young fruiting branches, then from 2 to 4 inches long, which 

 turned yellow and shriveled. 



It had been expected that the fruiting branches would cease to 

 develop as soon as the surrounding hedge of vegetative branches 

 grew up around them, for this had been indicated by the results of 

 previous experiments, but in this instance the abortion of the lower 

 fruiting branches took place before the vegetative branches had 

 grown tall enough to cast any shade upon the fruiting branches. 

 Thus, it becomes apparent that there is a spontaneous physiological 

 abortion of the young fruiting branches. 



In addition to the injuries that arise from the fact that the de- 

 velopment of vegetative branches results in unfavorable conditions 

 for the fruiting branches it is necessary to recognize another un- 

 favorable factor that acts directly through the plant, apart from 

 the dwarfing of fruiting branches that are surrounded and overshaded 

 by the vegetative branches. The conditions that favor luxuriant 

 development of the vegetative branches are in some way directly 

 inimical to the growth of the young fruiting branches, as though the 

 latter were actually cut off or poisoned. 



One suggestion is that the plants have two distinct phases or 

 methods of performing their physiological functions, as well as two 

 distinct kinds of branches. In the young plants the vegetative func- 

 tions can evidently go on at temperatures that are unfavorable to a 

 continuation of the reproductive functions, but temperatures can 

 hardly be the only factor, for the fruiting branches of older plants 

 are not aborted by hot weather. 



The changes that often occur in the color of the foliage at the 

 beginning of the flowering season may be connected with the passage 

 from a vegetative to a reproductive phase. The two physiological 

 color phases, though often apparent in Upland cotton, are particu- 

 larly striking in the Egyptian. The foliage of young Egyptian 

 plants in a condition of vigorous growth has a very deep bluish or 



[Cir. 118.] 



