354 



SCIENCE. 



[Vol. XXII. No. 569 



ON BOOT HAIES. 



BY TH. JAMIESON, ABERDEEN, SCOTLAND. 



DuKiNG the past fifteen years, in the course of cavrjing 

 out a very large number of experiments to ascertain the 

 rehative effects of different forms of manure, and also, 

 which of the mineral chemical elements usually found in 

 plants are essential, no point was more strikingly illus- 

 trated than the inability of the plant to grow in the ab- 

 sence of phosjahorus, although all the other essentials of 

 growth were fully supplied. In its absence, the turnip 

 plant, for instance, reached the stage of forming only 

 leaflets, while neighboring plants, treated in every respect 

 in precisely the same manner, only that they were sup- 

 plied with phosiDhorus in addition, develo]3ed large 

 plants, jdelding a crop of about 30 tons per acre. No 

 laboratory or lecture room experiment could be more ef- 

 fective than the positive and negative results shown by 

 two such plots, side by side, and these evidences have 

 been abundantly rejjeated annually. 



In following out an inquiry bearing on this remarkable 

 action, a special microscopic examination of root hairs was 

 suggested; sjaecial in respect of introducing various con- 

 ditions of light and shade, even approaching darkness, as 

 well, of course, as adjustments of the focus under various 

 degrees of light. This is specially mentioned in order to 

 indicate that the feature on root hairs about to be ex- 

 plained is such as might easily escape notice in an ordin- 

 ary examination. An unlooked-for structure was thus 

 detected, as a consequence of attention being so long con- 

 centrated on the tip of the hair and of gazing continually 

 on the spot under cautious and slight alterations of both 

 light and focus. It was seen that there was a well defined 

 aperture. The aperture in the first case of detection was 

 so clearly defined, and moreover seemed so clearly con- 

 tinuous with the inner membrane or tube of the hair cell, 

 that no doubt was felt that there was an aperture. Pos- 

 sibly it would not have been discerned had it not 

 been on an unusual part of the hair, viz. : a little be- 

 low the point, so that the point formed a kind of cap. 

 As a rule, however, the ajserture is at the point. 



So necessary is it to examine the root hair under vary- 

 ing conditions of light and focus, and also to travel 

 along the inner lining of the tube with the eye till it 

 reaches the point where the aj)erture ought to be, and so 

 frequently is the aperture turned away from the point of 

 view, that one familiar with the process can easily under- 

 stand how any one not so familiar might rise from the 

 examination and feel satisfied that the hair is, indeed, a 

 a closed tube. Only persistence to continue, till the in- 

 experienced observer falls upon a suitably placed hair, is 

 followed by success. 



After having observed so satisfactorily the first aper- 

 ture, much time was spent during three years in exam- 

 ining the hairs of a large number of plants, and al- 

 though from the state of the plant roots, and the condi- 

 tion and position of the hair, the aperture has frequently 

 not been detected at the first examination, yet by an- 

 other selection and persistent examination the aperture 

 has been found without exception in the case of every 

 plant examined. 



On examination at this stage of the writings of the 

 niore emiuent botanists on the subject, it was found that 

 in few of these treatises is the detailed form of the hair 

 gone into with sufficient minuteness. 



The works of De Bary, Duchartre, Olivier, Gasparina, 

 Van Lieghem, Sachs, Vines have been referred to. 



The essential and accepted character given in all these 

 works is: a complete and closed cell, thread-like in form 



and broadened at the base, where it is continuous with, 

 and forms part of, the epidermis. 



The more recent works by Schwartz, Zacharias and 

 others dealing more ^particularly with root hairs have been 

 examined, but the idea of an aperture does not seem to 

 have occurred to them, and the negative evidence, of 

 course, is not of any significance. 



Ileferring now to the function of hairs as bearing on 

 an aperture. None of the writers on the minute struc- 

 ture of hairs dej)arts from the idea that the hairs are 

 closed cells, or, as Sachs describes them, exceedingly deli- 

 cate walled narrow tubes. 



By accepting this view a difficulty arises. It has hith- 

 erto beea found necessary to advance some explanation, 

 for the well-known fact that the insoluble matter, such as 

 phosphates, is assimilable by plants. Sachs says in expla- 

 nation that these insoluble matters are without doubt dis- 

 solved in the thin layers of water which surround the 

 particles of soil, basing this inference on the fact that 

 water running off from the drained pipes of tilled soil 

 contains these substances; but he infers further, that 

 " since the nutritive materials clinging to the jjarticles of 

 soil are not soluble, or but slightly so in water, the roots 

 must themselves effect the solution." This seems to be a 

 kind of forced conclusion, i. e. , as the insoluble matter 

 does get in, the jDarticles must be dissolved, and, he as- 

 serts, without, however, giving grounds for it, that this 

 solution is accomjslished by means of the extremely thin 

 membrane of the root hair being permeated with an acid 

 fluid. Now, it is obvious that, it being once accepted 

 that the root hair is a closed tube, and that side by side 

 with this acceptance is placed the well-known fact that 

 plants make use of insoluble matter, it becomes a neces- 

 sity to assume, and it appears little more than an assump- 

 tion, that the plants obtain their solids by the action of 

 an acid. The usual statement is, not that the plant roots 

 make use of an acid, but that they must make use of an 

 acid, thus indicating that there was no other way of get- 

 ting over the difficulty. 



Van Tieghem also says that the roots set free an acid 

 liquid which bathe their surface. He, however, under- 

 mines that statement by summarizing the functions of the 

 root as a threefold action on the soil: 



First — On the gases, by absorbing oxygen and disen- 

 gaging carbonic acid. 



Second — On the water and dissolved matter, by absorb- 

 ing them. 



Third — On the solids, by dissolving them. 

 Now, it is evident that if the root acts so as to disen- 

 gage carbonic acid, that acid alone is sufficient to account 

 for the reddening of the litmus; and this circumstance 

 takes away the support that such acid reaction might 

 seem to give to the assumption that the plant forms an 

 acid to dissolve the mineral food, unless, indeed, the dis- 

 solving acid be simply carbonic acid, in which case it 

 would be uncertain whether the acid is there to dissolve 

 insoluble matter, or is there as a simple j)roduct of de- 

 composition. Vines asserts, however, that the reddening 

 is permanent, and therefore is not due to carbonic acid. 



Considering the slight evidence thus provided by Sachs 

 and Van Tieghem, and that no observers seem to have 

 found any special acid in the root, but simply acidity that 

 may be accounted for by decomposition of the plant, or 

 of organic matter in the soil, the dissolving action of the 

 root hair seems to be little more than an assumption ren- 

 dered necessary as an explanation of the well-known fact 

 that insoluble matter is assimilated by the plant. 



A difficulty in accepting the passage of solid particles 

 by an aperture may seem to be presented by the consid- 

 eration that, if solid particles enter the hair tip by an 



