108 



THE AMERICAN MONTHLY 



[Jane, 



the under side in liomologous parts, 

 is the hairy side. If both sides are 

 hairy this side will be the more so. 

 This, as I have already said, I am 

 inclined to refer to the influence of 

 light as a general principle, though 

 the fact that the hairiness of sepals 

 and petals is still on the outer side 

 (or the side corresponding to the 

 lower side of the leaf), does not seem 

 to be directly explainable on this 

 theory, but seems to be indirectly 

 connected with it, through the mere 

 homology of the parts. 



Another very obvious fact as to 

 distribution, is that hairs are most 

 abundant upon the mid-rib and the 

 largeir fibro-vascular veins. When 

 they do not exist at all upon 

 other parts, they are often abun- 

 dant upon these vessels, and the 

 mid-rib is seldom absolutely hairless. 

 It is one of the most striking points 

 in connection with this subject, that 

 hairs commonly spring from the sur- 

 faces of fibro-vascular bundles, or are 

 more or less directly connected with 

 them. In most plants this character- 

 istic is plainly seen, but in many it is 

 obscured by the great profusion of 

 hairs ; and in some, though not hid- 

 den, it is not marked. I believe, 

 however, that there is an essential 

 relation between hairs and the fibro- 

 vascular system, which I will refer to 

 more specifically by and by. 



What I have said as to the distri- 

 bution of hairs, is generally true also 

 of glands. Indeed, this is to be ex- 

 pected from the fact that hairs and 

 glands are only different develop- 

 ments of the same organ, as it has 

 been already stated. 



Glands exist under every form, 

 from a mere epidermal cavity con- 

 taining an essential oil, as in Mag- 

 nolia glatica (the White Bay), or Hy- 

 tiericuvi parvifloru7n, to the complexly 

 specialized, secreting and absorbing 

 tentacles of the Droseracese. Between 

 these extremes we find a mere orifice 

 emitting a drop of resin or gum — as in 

 Gayhissacia — the half-external, half- 

 internal, multicellular, rosette-like 



gland of Rhododendron fef-rtigifieum, 

 the sessile, but quite external gland of 

 Myrica or Callicarpa, the glass fun- 

 nel of Chenopodium, the pedicellate, 

 spreading, flower-like gland of Hho- 

 dodendroji Nuttallii; the short, gland- 

 ular hair of the tomato or Rhodora 

 or of Pluchea j and the long, stinging 

 hair of Urtica. As has been inti- 

 mated already, the hairs of Croton 

 caramba and the glands of Caiya 

 glabra are so nearly alike in appear- 

 ance that they may be regarded as 

 connecting links. 



One of the characteristics of all 

 epidermal appendages is the tendency 

 to a deposition in them of silica or 

 of lime, particularly of silica. In the 

 Diatomaceae the siliceous frustule is 

 the largest part of the whole organ- 

 ism ; and in the Equisetacese and the 

 Graminese the deposit of silica in the 

 epidermis and cuticle is of no small 

 amount or importance. The peculiar 

 form of the deposit in and upon 

 many kinds of hairs is a distinguish- 

 ing mark, and in many it is so general 

 and abundant that an indestructible 

 cast of the hair remains with the cuti- 

 cle, after maceration or burning of 

 the leaf on which it is found. 



This is particularly the case with the 

 large and striking stellate hairs of the 

 Deutzias. In these hairs as v/ell as in 

 many others (as for example : those of 

 Onosmodiiim^ Lithospermum, Bentha- 

 viia and Astragalus)^ the silica is dis- 

 posed in apparently granular masses, 

 distributed over the surface of the hair, 

 giving it the appearance of the larger 

 and coarser spicules of some of the 

 Gorgonidse. 



Under a high power these grains 

 have sometimes seemed to me more 

 like irregular truncate cones, or like 

 the deposits of silica or lime which 

 form on a larger scale around the 

 mouths of geysers and hot springs, 

 and I have therefore imagined that 

 perhaps they were actually forma- 

 tions about orifices from the interior 

 of the hairs, though I have never been 

 able to demonstrate, to my own satis- 

 faction, any suchopening through them. 



