^4 INFLUENCE OF CHEMICALS 



The form and size of the leaves and stems of plants growing 

 in soil rich in alkali or saline matter are deeply affected by these 

 substances. Sexual and asexual reproductive processes may be 

 called up or suppressed by the influence of different compounds. 

 Recent investigations by Loeb show that after the stimulation of 

 eggs of some of the lower animals by means of certain magnesium 

 and sodium compounds the eggs would develop as if they had 

 been fertilized or received the male reproductive element, and 

 Wilson has produced important variations in the primary proc- 

 esses of division of nuclei, and cleavage of the cytoplasm, by the 

 use of various chemicals. 1 Among the most singular changes 

 in form as a result of chemical action are galls or excrescences 

 formed on various plants as the result of a puncture and deposit 

 of eggs by insects and other animals. The deposition of the egg, 

 and the development of the larvae is undoubtedly accompanied 

 by the formation of an enzyme by the parent and its deposition 

 with the egg, or by its formation by the egg or larvae. In any 

 case the action of this enzyme exercises a stimulating effect that 

 causes the host plant to construct various abnormalities known 

 as galls. 



The rosettes formed on the tips of branches of willows, and 

 the galls of the oak are familiar examples of such action. 

 Kraemer has found that the changes in the tissues of the gall do 

 not cease with its separation from the plant on which it is borne, 

 but that the larvae of Cynips inhabiting the gall of the oak may 

 induce changes in the character of the cell contents, by which 

 gallic acid is manufactured at the expense of the starch. 2 



1 Livingstone, B. E. On the nature of the stimulus which causes the changes of 

 form in polymorphic green algae. Bot. Gazette. 30 : 289. 1900. 



Duggar, B. M. Physiological studies with reference to the germination of certain 

 fungous spores. Bot. Gazette. 21 : 38. 1901. 



Loeb, J. Artificial parthogenesis in sea urchins. Science, n : 612. 1900. 



2 Kraemer, H. Origin of tannin in galls. Science, 12: 583. 1900. 

 Kuster, E. Beitrage zur Gallenanatomie. Flora, 87 : 117. 1900. 



