LIFE HISTORY OF TIMOTHY 49 
veloped, and florets bloomed in very much the same manner as on 
timothy plants in meadows during the longer days of late spring 
and earty summer. 
DIFFERENT PHASES OF GROWTH IN RELATION TO PHOTO- 
PERIODISM 
Different phases in the growth of some plants respond to differ, 
ences in the daily period of illumination in different ways (11, p. 
911-919; 36, p. 314)- In timothy three distinct gradations in as 
many different phases of growth, in response to variations in the 
daily period of illumination, were observed during the course of 
this experiment. 
The growth of the leaves is affected relatively little by variations in the 
length of the period of daily illumination within the limits described for these 
experiments. 
The growth in length of the stems does not take place under the minimum 
period of illumination used in these experiments, i. e., 7 hours each day ; 
yet elongation of the internodes of the culm does occur several weeks earlier 
in the greenhouse, where normal conditions of lighting exist and where other 
conditions permit continuous growth to take place, than on plants growing in 
the field. 
The process of the development of the inflorescence is very sensitive to the 
length of the daily period of illumination. Heads did not appear, nor did 
florets bloom, on plants which had made continuous growth in the green- 
house with the natural period of illumination until at practically the same 
time in the spring when these processes took place on plants which had grown 
under normal conditions in the fields. 
SUMMARY 
A timothy plant is composed of all of the growing shoots which 
have developed either from a seed or from the detached vegetative 
part of another plant. In a plant several years old there may be a 
number of closely associated shoots or groups of shoots which have 
no vital connection with one another, but which, nevertheless, repre- 
sent branches which have originated from the same primary shoot. 
The position of a timothy seedling tends to become adjusted, in 
relation to the surface of the soil, as the seed is sown at different 
depths, ranging from the surface down to about 1 inch below it. 
Within these limits, through elongation of the mesocotyl, the base 
of the primary shoot of the plant develops near the surface of the 
soil, irrespective of the depth at which the seed was sown. 
When timothy is growing under natural conditions the seeds 
mature, fall to the ground, and a large proportion of them may 
germinate during the late summer months. A shoot originating from 
a seed which germinates at this time continues its growth until the 
following season. If an inflorescence develops on it, seeds will 
mature in midsummer, and within a few weeks or months the shoot 
becomes entirely dry, about one year or a little more than a year 
after it began its growth. If a timothy seed is sown in early spring 
and if conditions are favorable for growth, the primary shoot of the 
plant may produce seeds and complete its growth in the same 
season. 
A timothy plant continues to perpetuate itself indefinitely through 
the growth of new branches from buds in the axils of leaves, gen- 
4730°— 27 4 
