1901.] NATURAL SCIENCES OF PHILADELPHIA. 365 



strong in comparison with the variety. The Kihuarnock Weeping 

 "Willow is weak in comparison with Salix caprea, its parent, and 

 this is true of all the Aveeping trees in gardens — they are all in 

 various degrees more slender and delicate than the normal forms 

 of the same species. 



The ability to overcome gravitation has been lost, iu proportion 

 to the lessened degree of energy. 



How does this view account for the case of the incurving of 

 branches that have become decumbent ? 



It seems like a mere restatement of the fact to say that the 

 incurving branch has simply regained a power to successfully lesist 

 gravitation it had never wholly lost. When we note, however, 

 that these incurves are all methodical, and onlv occur when they 

 are evidently beneficial to the plant, we may infer that energy 

 itself is not blindly directed, but is under the control of a life- 

 power within the plant that is able to strengthen a weak position 

 when it is for the general good. AVe see this when it undertakes 

 to heal a wound ; we only extend our view of this power to meet 

 these new cases. 



In conclusion, trees have the power, not merely to grow into 

 various forms as it is usually understood, but to bend mature 

 branches when exigencies require it; and this display of power 

 results from varying degrees of energy employed by i^lants in 

 their struggle with gravitation. 



