CHAPTER II 



GENERAL REMARKS ABOUT THE MATERIAL AND THE 



EXPERIMENTS 



The organism used for the experiments was the plant Bryo- 

 phyllum calycinum, which was raised in numerous specimens 

 from a few leaves of this plant which the writer received nine 

 years ago from Bermuda. When a leaf of this plant is detached 

 from a stem and put on moist soil (or suspended in moist air) 

 each one of its notches may give rise to roots and shoots from 

 which new plants develop (Fig. 14). It has been stated that this 

 is the usual way by which the plant propagates. The plant 

 consists of a straight unbranched stem bearing 2 leaves in each 

 node which grow and reach a large size. In the greenhouse the 

 young leaves are thin in summer and become fleshy in winter. 

 The plant sheds only the older leaves, i.e., those nearest the base, 

 while new leaves are continually formed at the apex. As a 

 consequence the plants as they exist in the greenhouse have a 

 straight unbranched vertical stem which may be as thick as a 

 thumb and which may reach the height of 2 meters or more, 

 with leaves in the upper nodes near the apex, while the lower 

 nodes are free from leaves. Each node has, as stated, 2 leaves 

 and the axis connecting the 2 leaves in one node is always at 

 right angles to the axis connecting the 2 leaves in each of the 2 

 adjacent nodes. Only a small number of plants in the green- 

 house produced flowers and these plants were exposed to the 

 strongest light; the majority, kept in parts of the greenhouse 

 where the illumination was not so good, never produced flowers. 

 The plants used for the experiments belonged to this latter class. 



The care these plants require is of special importance. In the 

 greenhouse they are hable to suffer from insects, especially plant 

 lice, from which it is necessary to keep them free. A second 

 factor of importance is that these plants did not thrive in the 

 rooms of the laboratory where illuminating gas was used or where 

 people smoked. No quantitative experiments on regeneration 

 could be made with any degree of satisfaction in the laboratory 



9 



