232 The Philippine Journal of Science 1916 



The chief reason for this very considerable difference is not 

 the rate of growth of active plants, but is rather the fact, that 

 after the middle of the time of experiment there was a decided 

 tendency for the plants in darkness to die at the tips. This was 

 perhaps due to the dry atmosphere, perhaps to darkness itself. 

 The death of the tip was usually followed by the appearance of 

 branches. The plants in darkness had usually several axes, 

 either by the branching of the shoot, or by the production of a 

 number of successive shoots from the root; while in light, the 

 plants of most varieties produced a single shoot, which did not 

 branch during the period of the experiment. What would ob- 

 viously be expected, was true — the plants with one shoot reached 

 a greater length than did equally thrifty plants with several 

 shoots of which only one was measured. 



The possibility has just been suggested that the darkness is 

 itself responsible for the blasting of the young tips and their 

 replacement by branches. In the course of the experiment, it 

 happened to nearly all of the plants, which were first to germinate 

 and grow vigorously, that the vigorous shoots gradually grew less 

 rapidly and presently ceased to grow altogether. This happened 

 sooner in darkness, but eventually to many of the plants growing 

 in light. My first impression in the case of the plants in light, 

 which in several cases reached a length of nearly, or quite, two 

 meters before growth ceased, was that the store of food was 

 becoming exhausted or that the distance to which food might be 

 transported from the root to support activity at the growing 

 point had been reached or exceeded. However, it presently 

 developed, that in every case of this kind one or more branches 

 developed soon after the cessation of growth of the first tip and 

 that at least one of these branches grew as actively as the main 

 shoot had previously done and presently exceeded the main shoot 

 in length. The experiment was continued long enough so that 

 some of these branches in their turn ceased to grow in the same 

 manner and were likewise outgrown by other branches. The 

 total length from root to tip of branch was in a number of cases 

 more than twice that of the main shoot. 



The plants in the laboratory, although spoken of as exposed 

 to light, were not illuminated as plants are likely to be in nature. 

 It occurs to me, that with anything less than normal illumination 

 it may be natural for the tip of any one stem or branch to cease 

 to grow after a time, unless it comes under conditions quite 

 favorable to development as a permanent main axis of the plant. 

 Under these conditions, the attempt is made next with a branch 

 which at first, at least, follows a different course from the parent 



