CHEMICAL BASIS OF PLANT FORMS 241 



Zinc l is also a frequent constituent of plants growing about 

 zinc mines. Certain marked varieties of plants are peculiar to, 

 and appear to have been developed by such soils, as the violet, 

 var. calaminaris, and penny- cress. In the leaves of the latter 

 plants, thirteen per cent, of zinc oxide was found ; in other plants 

 from .3 per cent, to 3.3 per cent. 



From the investigations of Baumann, 2 insoluble zinc salts in 

 the soil are harmless to plants. All plants excepting the Coni- 

 ferae speedily die in a solution containing 10 mg. zinc to the litre, 

 though traces of zinc in solution are harmless. 



The specific action of zinc on the vegetable organism consists 

 in a destruction of the chlorophyl coloring- matter and a con- 

 sequent stoppage of the whole process of assimilation. 



Experiments 3 on maize, oats, buckwheat show that arsenic 

 attacks the protoplasm of the cell and destroys the power of 

 osmose by the roots. 



Sulphates occur in the cell sap of organs where chemical 

 changes are rapidly taking place, and are doubtless formed in 

 connection with the decomposition of proteids. Phosphorus 

 occurs in actively growing cells in the most various plants. It 

 has been found present in the green coloring- matter of the 

 leaves and is always found in relation with living protoplasm. 

 Schumacher 4 holds that the chief work of the alkaline phos- 

 phates is the acceleration of the diffusion of these difficultly 

 diffusible albuminoids. 



Calcium is especially abundant in the leaves of green trees, 

 and it cannot be replaced in the food of green leaves by any 

 other metal. It can be replaced by strontium, 5 barium, or mag- 

 nesium in the food of certain fungi. Magnesium 6 resembles 

 lime in many points, but is present in larger quantity in the 

 stem and grain, and not in the leaves of the maize plant. 



1 A. Braun and Risse (Sachs, Exp. Physiologic, 153). 



2 Landw. Versuchs-Siat., xxxi, 1-53 (Jour. Chem. Soc., 1884, p. 1408). 



3 F. Nobbe and others. Landw. Versuchs-Stat., xxx, 381-422 (Jour. Chem. 

 Soc., 1884, p. 1409). 



4 Physik der Pftanze, p. 128. 



5 Naegeli. 



8 R. Hornberger and E. V. Raumer, Bied. Centr. Bl., 1882, 837-844 (Jour. 

 Chem. Soc., 1883, p. 491). 



