278 GENERAL PLANT PATHOLOGY 



Sulphur and phosphorus are of some value in the production of 

 albuminous substances by the plant, and in the soil they exist mainly 

 as calcium sulphate and calcium phosphate. Phosphorus is in some 

 way associated with the formation of the crystalloids, globoids and 

 aleurone grains of the plant. Some soils are poor in phosphorus, so 

 that the agriculturist must supply phosphates. The deficiency of 

 phosphorus is seen in the production of a red coloration in plants. The 

 leaves are blotched with red and later the spots become dark brown. 

 The formation of flowers and seeds is partially inhibited. The absence 

 of sulphur is manifest in the poor development of the whole plant and 

 in the reduction in the amount of fruit produced. 



Nitrogen enters largely into the living substance of the plant, 

 protoplasm. It is stored in the form of protein granules and aleurone 

 grains. In the life of the plant, it is concerned in the building of young 

 tissues, and in the metabolism of plants, it appears in the form of aspar- 

 agin which in the soluble state is conducted through the bast portions 

 of the vascular bundles from one part of the plant to another part. 

 Some plants have a peculiar relationship to nitrogen. Such are the 

 leguminous plants, which are provided with root nodules, where there 

 are nests of bacteria. These bacteria can utilize free atmospheric nitro- 

 gen and later in the involution form as bacteroids, they are absorbed 

 by the green plant which is thus enriched with nitrogen. During the 

 period of entrance of bacteria into the root hairs, the young seed- 

 ling goes through a period of nitrogen starvation, when it appears 

 to flag, but later, it regains its active growth and vitaUty when the 

 nodules have been formed. Contrasted with the same leguminous 

 species without nodules and when the root systems alone take up 

 nitrogen in the form of nitrates, the nodulated plant is larger and 

 stronger in every respect. 



A deficiency of nitrogen in the soil can be detected in the case of 

 Indian corn and other agricultural plants by a general paling of the 

 green color, so that in some cases the plant becomes yellowish-green. 

 Klebahn^ indicates that the leaves of beets, buckwheat and potatoes 

 assume a yellowish color with a deficiency of nitrogen, and as the leaves 

 dry, they become yellowish-brown. The prothallia of ferns in a nitrogen- 

 free nutritive solution do not form meristem or archegonia. Excessive 

 suppUes of nitrates in their appUcation to cultivated fields stimu- 

 » Klebahn, Prof. D. H. : Grundziige der AUgemeinen Phytopathologie, 1912:11. 



