60 STUDIES IN THE VEGETATION OF THE STATE 



cells of the growing point perish. But when the plant has 

 reached the flowering stage, the last part of the plant to die 

 is the immature fruit, the order of dying for the other organs 

 being the same as before. 



Plants which propagate by means of bulbs and tubers often 

 suffer drought with only a temporary injury. Sagittaria 

 latifolia continues its existence principally by means of tubers. 

 One of the first things a «aggitaria plant acomplishes after 

 two or three leaves appear is to send out an underground 

 shoot or stolon which forms at its terminus a bulb. 

 These bulbs are usually mature long before the plant pro- 

 duces flowers and fruit, and when a young plant suffers from 

 a period of drought all the reserve energy of the leaves is 

 apparently transferred to the tuber which matures as the 

 other parts of the plant die. Bulbous plants behave in a 

 similar way: a young bulb is formed which matures as the 

 other portions of the plant dry up from loss uf water. Bulbs 

 and tubers are very resistent to the effects of dry soil and 

 may retain their vitality for months under conditions of 

 most severe drought. 



Woody plants like trees and shrubs usually have roots 

 which penetrate the earth to a great depth. When such 

 plants die from drought, the root is the last portion of the 

 plant to die. The same appears to be true in case of most 

 pleiocyclic herbs, having either fibrous roots or a woody tap 

 root. 



In case of death from sudden drought , such as occurred 

 with the plants placed in the xerophytic atmosphere of the 

 laboratory, in some monocyclic herbs the root was the last 

 organ to die. The excessive evaporation from the leaves 

 hastened the death of the stem and growing point. Drought 

 rarely takes place so suddenly in nature. 



The root seems by far the most adaptable part of the plant, 

 and the leaves stand next in order. Plants growing in dryer 

 soil usually have proportionately larger root systems, pro- 

 viding the degree of dryness does not become so excessive 

 as to prevent the development of the plant. In the case of 

 mesophytes in nearly every instance noted, excessive water in 



