92 
WILLIAM SEIFRIZ 
other environmental changes may seem as far-fetched as to ascribe to 
chmate or food the periodic appearance of the seventeen-year locust which 
has this year (191 9) infested certain regions of our country. It is however, 
quite possible that the duration of the life cycle of plants exhibiting sexual 
periodicity is the direct result of certain known, present or past, stimuli. 
An apparently very clear example of such an association between season 
and periodicity is seen in the life cycle of annuals which flower and die at 
definite seasons of the year. But one can not always be certain that the 
most evident and seemingly controlling factor in such a case is the one at 
present active. A native annual in the temperate zone commonly rests in 
winter, germinates in the spring, fruits in summer, and dies in the fall. 
This sequence of events one is likely to attribute to the sequence of the 
seasons. Yet most annuals if grown in a greenhouse where seasonal changes 
are non-existent (except as to light) can, by sowing of seeds at the proper 
time, be made to fruit in any chosen month of the year without regard to 
seasonal conditions out of doors. Thus are the successive steps, from ger- 
mination to death, in the life span of an annual grown in a greenhouse 
accurately maintained without evident relation to any external controlling 
factor. That is, the annual germinates, fruits, and dies in the same interval 
of time that it always has required, and does this in an environment quite 
different from the seasonally progressive one of its natural habitat. This 
behavior seems clearly to belie the validity of the assumption that the 
present seasonal round determines the duration of each phase of the develop- 
mental cycle, and thus of the cycle as a whole. 
There are reported, however, examples of the flowering of plants being 
regularly brought on by such external factors as moisture. The following is 
such an example cited by Morris (5): "A prolonged drought in India is 
often accompanied by the flowering of the common bamboo, and on this 
account the natives associate the two phenomena in a manner which is 
emphasized by the fact that the bamboo grain during seasons of drought has 
provided them with the only available means of support." According to 
Ridley (cited by Schimper, i) two species of Hopea and four species of 
Shorea blossom with great regularity every sixth year. These cycles are 
said to coincide with dry years. Morris (5) believes that the long intervals 
at which the flowering of Chusquea takes place probably depend "for their 
exact length upon the aspect of the prevailing seasons." Weather reports 
from Cinchona show, during the years preceding the recent flowering of 
Chusquea, no pronounced digression in temperature from the general 
average. The rainfall was unusually heavy for two years immediately 
preceding the flowering of Chusquea. It is hardly likely, though possible, 
that an over-abundance of rain should bring on a flowering period in Chus- 
quea in Jamaica and drought be the cause of flowering of another bamboo in 
India. 
Further proof against the theory that time of flowering is determined by 
