130 



THE AMERICAN MONTHLY 



[July, 



In the first place, the mere mor- 

 phology of these structures confirms 

 the idea of their being truly hairs. 

 In their outlines they so closely 

 resemble some of the external hairs 

 with which we are familiar (for in- 

 stance those of the genus Arabis), 

 that their analogy is at once suggest- 

 ed to the observer. They seem, 

 however, to be always unicellular 

 growths, and transverse sections 

 show them to be hollow. Over their 

 surfaces are scattered the grains of 

 silex, so characteristic of other hairs, 

 and made particularly familiar to us 

 by the hairs of the Deutzias. If one 

 wishes a striking demonstration of 

 the mere resemblance of these inter- 

 nal hairs to better known external 

 hairs, he has only to split the petiole 

 of Nuphar or JVytup/nea by tearing, 

 and view it with the binocular as an 

 opaque object. This, of itself, will 

 be convincing to most persons ac- 

 quainted with the peculiarities of leaf- 

 hairs. 



But, aside from configuration and 

 other merely morphological consider- 

 ations, the mode of distribution of 

 these internal hairs is almost precisely 

 like that of external hairs. If we 

 take a thin section of a leaf of Nym- 

 phiea^ cut parellel to its surface, and 

 examine it as a transparent object 

 (still better if we illuminate it with 

 polarized light), we shall see that 

 these internal hairs, like external 

 ones, are associated with the fibro- 

 vascular system ; and toward the 

 margin of the leaf, where the tissues 

 are thin and the veins small, we shall 

 find that the hairs exist only upon the 

 veins and not between them. This is 

 quite in accordance with what we 

 know of the habit of all hairs, as I 

 have already explained. 



If we take a transverse section of 

 the leaf of Nymphaa or Nuphar, cut 

 across the mid-rib, we shall be struck 

 by another fact connecting these in- 

 ternal hairs with the epidermal sys- 

 tem. We shall at once notice that from 

 the upper side of the leaf — which is, 

 under common circumstances, the 



only side exposed to the air, and is 

 consequently the only side possessing 

 a true epidermis — these hairs spring 

 like stumps of trees in an inverted 

 field. From end to end of the sec- 

 tion they will be observed planted 

 close together, their pedicels im- 

 bedded in, or forming a part of, the 

 epidermal layer, and their branches 

 spreading downward and inward 

 through the underlying parenchymal 

 tissue. This is very marked in 

 stained sections, in which the hairs 

 take a darker color than the sur- 

 rounding tissues ; but in an unstained 

 section, polarized light differentiates 

 the structures quite as well as the 

 elaborate, double-staining process now 

 so commonly employed. It is to be 

 noted that this arrangement of the 

 hairs is confined to the upper or epi- 

 dermal side of the leaf, and that no 

 similar arrangement is to be seen at 

 any other part. The distribution of 

 the hairs on the interior of the petiole 

 of the water plants is somewhat 

 different from their arrangement on 

 the interior of the leaf, but it is 

 closely analogous to the arrangement 

 of hairs upon the exterior of the 

 petiole of land-plants. 



I have referred to the fact that 

 these internal hairs are good objects 

 upon which to use polarized light ; 

 ,and this is a point of no small im- 

 portance in the argument for their 

 being actually hairs. To any one 

 acquainted with the behavior of veg- 

 etable tissues with the polariscope, 

 particularly of vegetable hairs, the 

 manner in which these internal struc- 

 tures of the Nymphasaceae are affect- 

 ed by polarized light is strong con- 

 firmation of their claim to be regard- 

 ed as epidermal organs and true 

 hairs. The way in which they take 

 different colors in the process of 

 double staining, will be another 

 affirmative argument with those fa- 

 miliar with that process and its 

 effects. Suffice it to say in this connec- 

 tion, that these internal hairs behave 

 in precisely the way, and take exactly 

 the colors, that external hairs do. 



