794 



SCIENCE. 



[N. S. Vol. XVII. No. 437. 



involving the discriminant) to ascertain when 

 cubic equations had imaginary roots. 



Chas. Baskerville, 



Secretary. 



DlSCVI^Sloy ASD CORRESPONDENCE. 



ECOLOGY. 



To THE Editor of Science: I read with 

 much interest Professor Fernow's article, 

 bearing the above caption, in Science, April 

 17, an article attractively written and con- 

 taining many valuable suggestions. 



I do not propose to enter into the general 

 discussion outlined by the author, but shall 

 confine myself to the paragraphs on the soil. 

 It would not be right to allow so misleading 

 a statement as ' it is first of all to be con- 

 sidered that chemical constitution [of the 

 soil] plays probably only a small part or 

 practically none; the reliance of tree growth 

 on mineral constituents being relatively small' 

 to go without protest. 



The chief fact that is adduced in support 

 of this .dictum rests on the small percentage 

 of ash in the grown tree and its greater 

 abundance in the leaves and younger growth. 



The growth of a tree is as absolutely con- 

 ditioned by ' mineral constituents ' as by any 

 other fundamental factor of the environment. 

 Vines says : ' Thus the inorganic substances 

 absorbed by the roots pass into the cells of 

 the leaves where they are concerned in the 

 processes of constructive metabolism which 

 are in operation in those organs.' 



It is apparent that without this ' construc- 

 tive metabolism ' the materials of which the 

 chief part of the plant is composed, mostly 

 carbohydrates, could never be provided. 



One of the functions of the absorption of 

 water as such by plants is to secure the trans- 

 lation of these mineral elements from the soil 

 to the parts of the organism where their con- 

 structive work is to be done. 



Vines says : ' Only very dilute solutions of 

 salts can be taken up by the roots; as a con- 

 sequence, it is necessary that relatively large 

 quantities of water should be absorbed in 

 order that the plant may be supplied with the 

 salts which are important in nutrition.' 



The tree, during the whole period of its 

 growth, does not use from without a single 

 organic product. It gets its nitrogen in the 

 form of nitric acid, its carbon in the form of 

 carbon dioxid, its phosphorus in the form of 

 phosphoric acid, its hydrogen in the form of 

 water, and so on to the end of the nutrients. 

 The fact that mineral matters are exuded in 

 the leaves is no proof that they have not per- 

 formed or assisted in performing the most 

 important physiological functions. The ex- 

 cretion of a ' mineral constituent ' may even 

 be a proof of its importance in metabolism, as 

 is the case with a great part of the phosphorus 

 that is excreted from the body. Nature is 

 careful to provide a superabundance of the 

 most important substances. Because a tree 

 may take up only one millionth part of the 

 carbon dioxid which comes to it in the air 

 during- its period of growth, is no reason for 

 saying that this constituent of the air is of 

 little consequence in biodendry. 



1 Mineral substances not only are useful and 

 necessary in plant growth because of their 

 part in forming tissues, but also because they 

 stimulate by their presence the functional 

 activity of the vegetative cells. In other 

 words, they are condimental or katalytic as 

 well as constitutional. Although potash is 

 not a constituent of starch, it is thoroughly 

 established by indubitable evidence that in 

 the absence of potash in the plant blood starch 

 granules are not formed. 



The ions of mineral matter taken from the 

 soil and coursing through the circulating ap- 

 paratus of the tree perform useful and neces- 

 sary functions from the time they enter the 

 waiting mouth of the rootlet until they con- 

 gregate in the extremest tip of the reddening 

 leaf. 



The ' mineral hunger ' of plants is as well 

 known and recognized by physiologists as that 

 of animals, and the welfare of the growing 

 tree is undoubtedly as profoundly affected by 

 the soil element of its environment as by any 

 other. Experiments have shown the minimum 

 of any given mineral element of the soil which 

 will permit normal development, but such a 

 minimum only does so in case other mineral 



