Feb., 1923] SEIFRIZ CAUSES OF GREGARIOUS FLOWERING IO9 



solution of starch, etc. — some are undoubtedly susceptible to environmental 

 factors. Furthermore, the same phenomenon varies in different plants in 

 the readiness with which it can be influenced by surrounding conditions. 

 Thus, the winter's rest in some plants is easily altered, in others it can not 

 by any known artificial means be broken. Klebs first clearly showed 

 experimentally that periodicity in plants can be disturbed. In this lies 

 his contribution to biology. But when Klebs would have us believe that 

 all the activities of plants are to some extent determined by the outer 

 world, we question his right to do this in the face of his own experiments 

 since he found certain plants which could not be aroused from their winter's 

 rest (15). 



But even in those cases in which the normal periodicity can be disturbed, 

 the question arises whether or not the mere ability to alter the normal 

 rhythm of growth by changing the external environment is an indication 

 that this periodicity is actually the direct result of an environmental rather 

 than of a germinal factor. There are some striking instances in which the 

 normal alternation of growth and rest is upset but the plant suffers in 

 consequence. Disturbing the usual growth rhythm results in weakening 

 the plant's vitality. An excellent illustration of this exists at Tjibodas, 

 Java, where there is a small apple tree growing in the acclimatization 

 garden in the mountains. This temperate-zone tree has been growing in 

 the tropics for some twelve years or more, in a climate which has no pro- 

 nounced seasonal change. Its normal periodicity of growth and rest has 

 been disturbed but not done away with. The tree is undersized (four feet 

 high) and has never borne fruit. It stands there an unhappy specimen, 

 with, when I saw it, one branch in full foliage, another without any leaves 

 at all, and still another with well-developed buds. It seems to be having a 

 sad time trying to exist in a seasonless climate with an inherent periodicity 

 of growth and rest manifesting itself at different times of the year on different 

 branches. The periodicity is there. The seasonal cycle of temperate 

 regions would have determined when the rest and growth periods should 

 occur. In a tropical climate this seasonal guidance is lacking and the 

 normal rhythm of growth and rest is disarranged, but the inherent perio- 

 dicity is still evident. 



The fact that the winter's rest in plants can in many cases be disturbed 

 has led other workers than Klebs to come to rather far-reaching conclusions. 

 Thus Howard, as a result of some very extensive work on the treatment of 

 dormant woody plants for forcing them into growth, concludes that "all 

 of these forms of rest are caused by unfavorable external conditions" (9, p. 5). 



Just what the unfavorable conditions are which cause all kapok trees 

 {Ceiba pentendra) simultaneously to become completely defoliated each year 

 at Buitenzorg, where there is no pronounced seasonal change, it is difficult 

 to see. Even more striking is the case of Ceiba (C. occidentalis ?, the silk- 

 cotton tree) in Jamaica which annually loses all its leaves, but not simul- 



