PLANT DEVELOPMENT 



developing strange nervous symptoms, and 

 finally, unless supplied with food which con- 

 tains mineral support, dying with spasms 

 and suffocation. All manner of minerals go 

 to the manufacture of plants, — lime, magne- 

 sium, potassium, sulphur, iron, salts, alumi- 

 num, even copper, lead, antimony, zinc and 

 arsenic. Some plants, indeed, thrive in soil 

 which is rich in lead and zinc, while certain 

 pine trees which had their roots in a copper 

 soil were found to have taken up so much 

 copper that it made up one per cent of the 

 whole dry weight of the tree. It will be found, 

 too, if he can carry his investigations into 

 various lines, that silica lies in the leaves of 

 the plants, just as it lies in the quartz of the 

 mountains or in the deep lustrous depths of 

 the opal. He will find that when the summer 

 is waning a strange procession is in progress in 

 the trees, as the substances which have been 

 keeping the leaves green and fresh begin their 

 backward journey to the body and roots of the 

 tree, there to be stored up for the next sea- 

 son's service. Indeed, as one writer has shown, 

 this removal of the food supplies of the 

 leaves begins while the fruit is ripening, the 



71 



