MIXED CROP OF UNIFORM AGE. 53 



iusr to the loftv stature they attain. In evergreen forests trees of 



o J J o 



deciduous species tower above all the other growth. The great 

 advantage possessed by trees that can attain a greater height than 

 their immediate neighbours is, that they are able to resist almost 

 any amount of lateral pressure by always being free to develop in 

 another, the upward, direction. When such trees are also shade- 

 enduring, they enjoy a power of combined resistance and aggres- 

 siveness which makes them invincible, e. g. y deodar in mixed deodar 

 and oak forests. 



X. RELATIVE SUITABILITY OF CLIMATE. This is one of the 

 most important conditions in the struggle for existence, since in al- 

 most every case it determines the habitat of the various species, 

 and also the vigour of their growth. Climate is made up of many 

 factors, which it is best to consider separately: 



(a) Heat and frost. The influence of these factors in the mutual 

 struggle for existence is due chiefly to extremes, being very little 

 or scarcely appreciable within limited ranges of temperature. It will 

 suffice to take a single characteristic example illustrating this 

 statement. An examination of the subjoined table will show that 

 teak can flourish and attain its finest dimensions with an absolute an- 

 nual range in the open of as much as 134 Fah., provided the 

 minimum, does not descend below freezing point. As the absolute 

 range widens beyond the limit of 13-4 and the minimum sinks 

 lower and lower below freezing point, teak thrives less and less 

 well, until it disappears altogether with an absolute range of 150 

 and upwards, and with the minimum out in the open going down to 

 7 and more below freezing point. The lowest minimum temperature 

 under the open sky is almost the same at Seoul, Khandwa, Alla- 

 habad and Agra ; but, on the other hand, not only is frost more fre- 

 quent at the two latter places, but the evenings, nights and morn- 

 ings are generally many degrees colder in others words, the 

 absence of a sufficiency of heat is more prolonged and, therefore, 

 all the more sensible in its effects. For this last reason also, 

 although frosts are severer in Seoni and Khandwa, teak thrives 

 better there than in Jhansi. Until the lowest limit of temperature 

 is reached, a diminishing minimum manifests itself by a more 

 languishing vegetation ; when that limit is passed, to languishing 

 vegetation is added incapability of ripening seed. 



