Reserve Material of Plants. 201 



taining but little. The structure of the bark shows that the 

 intercellular spaces are large and frequent, the cells arranged with- 

 out order, irregular in form and size, and with relatively thin walls. 



We are now to inquire what relation, if any, these histological 

 conditions bear to the chemical constitution of the ash already 

 referred to, and particularly to the chemical results derived from 

 an examination of the tree restored to health by treatment. 



1st. In the normal plant, the full exercise of its functions of 

 growth and a normal histological condition occur, when potash 

 and chlorine are relatively in excess and lime is relatively wanting. 



2nd. In the diseased plant, the imperfect nutrition and distri- 

 bution of the reserve products, as also modifications of the cellular 

 structure, are associated with deficiency of potash and chlorine and 

 excess of lime. 



3rd. We are to inquire as to the relation in which the restored 

 tree stands to all of these. 



The chemical analyses already referred to show that, when the 

 restoration from abnormal to normal functional activity occurs, 

 the chemical constituents change their relations to those ob- 

 served in the normally healthy, i. e., the potash becomes in relative 

 excess. At the same time, the histological conditions show a corres- 

 ponding change, and as the new growth develops, the structure and 

 also the cell-contents assume precisely the conditions of develop- 

 ment and distribution found in the naturally healthy tree. 



These results may be regarded as fairly conclusive so far as 

 this particular disease is concerned, but we can as yet hardly 

 apply generally the laws here determined. However, the fact 

 here developed with reference to the distribution of the reserve 

 material will not apply with equal force to other trees or plants, 

 since there are very important variations in this respect, depen- 

 dent upon the physiological characteristics of particular species, 

 or at least of particular families of plants. Nor will the same 

 chemical elements, or the same chemical compound, be equally 

 efficient in all cases in determining a similar result, since here, 

 also, the effect is determined by specific physiological peculiarities. 

 This is well illustrated in the peach and the pear : both belong 

 to the same family Rosacea, yet the peach belongs to the group 

 Amygdalece, while the pear belongs to the group Pomece, 

 indicating at once specific physiological differences. And while 



