318 HOW CROPS GROW. 



new vegetable substance and increases in dry weight. 

 Mercadaiite's observations are therefore in accord with the 

 results of the investigations next to be considered. 



In 1869, Nobbe, Schroder, and Erdmann employed the 

 method of water-culture to make an elaborate study of 

 the influence of potassium on the vegetative processes, 

 and found that, all other needful conditions of growth 

 being supplied, in absence of potassiiim buckwheat 

 plants vegetated for three months without any increase in 

 weight — ^that is to say, without producing new vegetable 

 matter. Examination of these miniature plants demon- 

 strated that (in absence of potassium) the first evident 

 stage in the production of vegetable substance, viz., the 

 appearance of starch in the chlorophyl granules of the 

 leaf, could not be attained. The experimenters therefore 

 drew the conclusion that potassium is an essential factor 

 in the assimilation of carbon and the formation of starch. 

 They found that the plants were able to produce starfch 

 when potassium was supplied either asiohloride, nitrate, 

 phosphate or sulphate. The transfer of the starch from, 

 the leaves to the fruit, or its conversion into a soluble 

 form, appeared to require the presence of chlorine ; acr 

 cordingly, potassium chloride gave the best developed 

 plants, especially at the period of fructification. This 

 conclusion was greatly- strengthened by the observation, 

 repeatedly made, that the miniature plants which had 

 vegetated for three or four weeks without increase of 

 weig'ht, or growth other than that which the seedling can 

 make at the expense of the seed, began at once, on suit- 

 able addition of potassium chloride to the nutritive solu- 

 tion, to form starch, discoverable in all the chlorophyl 

 granules, and tlienceforward developed new stems and 

 leaves and grew in quite the normal manner. In Plate 

 I the appearance of some of the plants produced in these 

 trials is shown. la represents the average plant raised 

 in the normal solution containing abundance of potas- 



