166 



THE AMEEICAN MONTHLY 



[September, 



Botanical Gazette for March, 1881. 



I copy below some passages from 

 Prof. Arthur's paper which show that 

 he and I were unconsciously working 

 over some of the same ground at 

 about the same time ; and I am pleased 

 to find that his researches led him, with 

 regard to hairs being organs of the me- 

 tastatic process, to substantially the 

 same conclusion as my own. He says : 



" All the forms mentioned in this 

 article fall under one of two classes, 

 capitate or filiform. Trichomes of the 

 former class are inclined to be 

 glandular while those of the latter 

 are not. This accords well with their 

 distribution over the plant surface. 

 The filiform ones contain the more 

 highly vitalized protoplasm, as mani- 

 fested by its activity. They are situ- 

 ated on the parts of the plants which 

 are destitute of stomata and growing 

 rapidly, and consequently in need of 

 some other means of directly absorb- 

 ing water and oxygen from the at- 

 mosphere and soil. On the other 

 hand the capitate forms are on sur- 

 faces well provided with breathing 

 pores. The latter serve to absorb 

 oxygen during the earlier stages of 

 growth, while the stomata are ineffi- 

 cient. When the stomata perform 

 their allotted function, and the inter- 

 cellular spaces are free of sap and 

 protoplasm, these capitate trichomes 

 become glandular and are turned to 

 other service, or disappear. 



" Considered physiologically, trich- 

 omes are not indispensable to the 

 plant, yet in a small way frequently 

 .render important assistance. The 

 value of the root hairs is one of the 

 best known facts in botany, being 

 uniformly illustrated in general treat- 

 ises, and insisted upon in horticultur- 

 al essays on transplanting. Hairs on 

 many plants serve for protection 

 against detrimental changes of the 

 weather, the attacks of animals, etc., 

 but in Echinocystis the only trichomes 

 that could be considered protective 

 are those which roughen the leaves. 

 Upon rapidly growing parts (especial- 

 ly true, e. g., of young flower-buds) the 



abundance of delicate trichomes aids 

 in supplying oxygen to the tissues. 

 Stomata and air cavities perform this 

 office in the older portions, but in 

 parts newly formed the cavities are 

 filled with protoplasm and cell sap, so 

 as to prevent free circulation of air. 

 Moreover, a very rapid supply of oxy- 

 gen is required at this time to meet 

 the needs of metastasis by which the 

 increase of protoplasm and the for- 

 mation and multiplication of cells is 

 effected. The oxygenation of the 

 plant in such growing parts is some- 

 what analogous to that of some polyps 

 and worms having external fila- 

 mentous gills, while later it assumes 

 the more efficient internal respiration 

 corresponding to that of insects. 



" It has already been hinted that 

 there is a similarity of function be- 

 tween the hairs of growing shoots and 

 of young roots. Both subserve the 

 interests of the plant by increasing 

 the surface through which material 

 for the plant's sustenance and growth 

 may be absorbed. The character of 

 such material is determined by the 

 nature of the respective media in 

 which the organs vegetate — of shoots 

 it is gaseous, of roots aqueous." 



Wholesale Destruction of Acari 

 by a Fungus.* 



BY C. M. VORCE, F. R. M. S. 



In March last, while passing a heap 

 of stable manure, I kicked over a 

 piece of board lying on the heap, and 

 on glancing at the uncovered spot 

 my attention was attracted by an ap- 

 pearance as if very fine meal had 

 been sprinkled over the surface of 

 the manure. Supposing this to be 

 the spore-cysts of a fungus, I secured 

 a quantity of the supposed fungus in 

 situ. Under a pocket lens the sur- 

 face of the material was seen to be 

 thickly studded with minute, whitish, 

 globular bodies, very much like, but 

 somewhat larger than, the capsules of 



* Read before the American Society of 

 Microscopists at the Columbus meeting, 

 August, 1881. 



