75 6 



THE POPULAR SCIENCE MONTHLY 



phorus as an Original Element ? By Samuel 

 R. Percy, M. D. Philadelphia : Collins, 705 

 Jayne Street, 18*72. 



Report of the Committee on Climatol- 

 ogy, etc., of Arkansas. By Geo. W. Law- 

 rence, M. D. (Same publisher.) 



Twenty-first Annual Report of the Re- 

 gents of the University of the State of New 

 York, on State Cabinet of Natural History, 

 etc. Albany, 1871. 



Researches in Actino-Chemistry. Me- 

 moir Second. By John W. Draper, M. D., 

 LL.D. 



Australian Kinship. By Lewis H. Mor- 

 gan. 



Second Annual Report of the Board of 

 Commissioners of the Department of Pub- 

 lic Parks (New York City). 1872. 



Mysteries of the Voice and Ear. By 

 Prof. 0. N. Rood. New Haven : Chatfield, 

 1873. 



MISCELLANY. 



The Selective Power of Plants. 



Sheffield ScrENTtnc School, ) 

 New Haven, Conn., Feb. 25, 1673. j 

 Editor Popular Science Monthly. 



Dear Sir : In his interesting article on 

 " Spontaneous Movements in Plants," print- 

 ed in your January number, Dr. A. "VV. Ben- 

 nett remarks, page 284, that " the selective 

 power of plants, in absorbing from the soil 

 a larger portion of those ingredients which 

 are required for the formation or healthy 

 life of their tissues, is an absolutely unex- 

 plained phenomenon." Dr. Bennett says 

 further, " A striking instance of the liability 

 to consider a mere statement of an obscure 

 law in other terms as an explanation of 

 that law, occurs in an admirable treatise on 

 the growth of plants Johnson's ' How 

 Crops Grow.' " Then follows the subjoined 

 quotation from my book (the italics are Dr. 

 Bennett's) : " The cereals are able to dispose 

 of silica by giving it a place in the cuticular 

 cells: the leguminous crops, on the other 

 hand, cannot remove it from their juices ; 

 the latter remain saturated, and thus fur- 

 ther diffusion of silica from without becomes 

 impossible, except as room is made by new 

 growth. It is in this way that we have 



a rational and adequate explanation of the 

 selective power of the plant." Dr. Bennett 

 adds : " The ' rational and adequate expla- 

 nation ' seems to me, on the contrary, to be 

 merely a restatement of the selective power 

 of the tissues in other terms. Because the 

 tissues want the silica, is no explanation of 

 how they get it." 



Very possibly, Dr. Bennett holds me at 

 a disadvantage as the matter thus stands, 

 but I am, in fact, very seriously misrepre- 

 sented in the last sentence of his quotation 

 from "How Crops Grow." On page 363 of 

 the American edition, the reader may see 

 that the period which concludes Dr. Ben- 

 nett's quotation should be a comma, and 

 that the sentence, as I wrote it, first comes 

 to a conclusion after an important qualify- 

 ing clause, and reads, entire, as follows : 

 " It is in this way that we have a rational 

 and adequate explanation of the selective 

 power of the plant as manifested in its de- 

 portment toward the medium that invests its 



7'00ts." 



It appears that Dr. Bennett has inadver- 

 tently confused two quite distinct things. 

 He asserts, at first, that " the absolutely un- 

 explained phenomenon" is "the selective 

 power of plants in absorbing from the soil 

 those ingredients which are required for 

 their tissues." But, afterward, he declares 

 my " explanation " to be " merely a restate- 

 ment of the selective power of the tissues." 

 Obviously, the selective power of the plant, 

 as manifested toward the medium that in- 

 vests its roots, is one thing, and the selec- 

 tive power of the tissues toward the sub- 

 stances dissolved in the cell-juices is, or 

 in many cases may be, another. The for- 

 mer is what I offered a rational and ade- 

 quate explanation of. The latter I have 

 not ventured to attempt to explain. The 

 former is explained by being coordinated 

 with the well-ascertained facts of "diffu- 

 sion " and " osmose," and referred to estab- 

 lished, if not fully-developed, physical laws. 

 The latter belongs to the yet very obscure 

 phenomena of chemism, which are only 

 known to us imperfectly in some of their 

 results, and whose inner nature the recent 

 amazing progress of organic chemistry has 

 hardly begun to enable us to speculate upon 

 with any satisfactory degree of probability. 



Dr. Bennett writes of silica as one " of 



