420 WRIGHT : FOLIAR PERIODICITY 
and the growth in length of roots, and concludes that there 
is no season which does not set certain functions of the plant 
in activity. There is however a foliar periodicity of tem¬ 
perate zone vegetation which is obviously directly associated 
with the seasons. 
Periodicity in the Tropics. 
In the tropics there may or may not be a climatic periodi¬ 
city analogous to the seasons of temperate zones. In all 
tropical areas heat and light are intense, and these, together 
with the heavy rainfall of many places, result in a conspicuous 
growth of vegetation at most times of the year. Schimper 
stated that his observations in tropical districts, with an 
abundant rainfall at all seasons, convinced him that the life 
occurrences of the plant show a rhythmical change of periods 
of rest and activity. F 
The investigations of Sachs and Muller-Thurgau have 
whole of the life occurrences of the plant, but only resting 
periods for certain functions. g 
The tropical plants are just as subject toperiodical changes 
of rest and acttvity as the plants of cooler zones. 
Schimper asserted that where a marked elimatie periodi- 
Z jyZeifr taDCHOm 0t th6 Plant8 - ^ueneed 
thereby, the dry seasons operating in many respects like 
-r- “ 
i-iy r - - - 
rest and activity in everv h<> am0ant ° f 
approximately the same while i th* 8 ™ eration remains 
periodic increase and deire^! ““ nd Caae “ **» * 
