104 



THE AMEKICAiq MONTHLY 



[June, 



may be seen on the leaves of Clematis 

 erecia, Astr<igalus vesicarens, and of 

 Benthamia fragifera. 



Branched hairs are multicellular 

 hairs in which growth takes place in 

 many directions, or not entirely in one 

 general direction. Examples of this 

 mode of growth are found upon Alter- 

 nanthera lanuginosa, and upon Ver- 

 bascum thapsus and many others of the 

 Scrophulariacae. 



A variety of this species is the 

 radiate, in which the branching 

 is confined to nearly horizontal 

 planes. This form of hair occurs 

 upon the upper side of the leaf of 

 Shepherdia Canadensis, and upon many 

 of the Polypodiaceae. 



These branching modes of growth 

 (especially the radiate) give rise to 

 many of the forms commonly includ- 

 ed under the term stellate ; but I pre- 

 fer to reserve that name for unicellu- 

 lar, star-shaped hairs, such as are 

 found upon Deutzia, Vesicaria and 

 some species of Alyssum. 



Peltate hairs are those partly mem- 

 branous, partly radiate, scale-like 

 hairs, which occur upon all the Elcea- 

 gnacece, upon some of the Crotons 

 and upon Sida lepidota. 



I apply the term rosette to those 

 less scale-like, though nearly peltate, 

 hairs such as are found upon Croton 

 caramba. These differ from the pel- 

 tate hairs in having fewer lines of 

 radiating growth, and in being less 

 membranous or scale-like. They 

 approach closely to the forms of the 

 glands of Callicarpa, of Carya, or of 

 the Myricaceae. 



When several simple hairs are de- 

 veloped from adjacent epidermal 

 cells, I term them grouped. Some- 

 times these grouped hairs consist of 

 but two simple hairs in contact at 

 their bases, but often five or six or 

 more form a group which, when seen 

 from above, give the appearance of a 

 stellate form. Such stellately grouped 

 hairs are common among the Mal- 

 vacese and the Cistacese. In Helian- 

 themiim canum, var. genuina, we have 

 a good example of stellately grouped, 



short hairs, associated with simple 

 groups of two, three or four long 

 right hairs. 



Closely allied to this form is the 

 one which I call mammillate. In 

 this species what would be the cen- 

 tral hair of a group is fully devel- 

 oped, but the surrounding epidermal 

 cells are only partly developed into 

 hairs, most frequently just enough to 

 slightly raise them above the general 

 surface of the epidermis, thus produ- 

 cing a protuberance or mamma upon 

 the surface of the leaf, from the centre 

 of which the fully developed, simple 

 hair seems to spring. This is a char- 

 acteristic form amongst the Borra- 

 ginacece, and is most strikingly exhib- 

 ited on the leaf of Onosmodium Vir- 

 ginianmn. In some species, however, 

 all the hairs are aborted, and what 

 might otherwise be a group of 

 hairs, is only a group of partly 

 developed epidermal cells. This is 

 exemplified in Echifiacea angustifolia. 

 On the other hand, it happens in 

 some species that all the grouped 

 epidermal-cells, or a large number of 

 them, become fully developed hairs, 

 but only the central one grows per- 

 perpendicular to the surface of the 

 leaf, the others radiating about its 

 base in a nearly horizontal position, 

 or at an acute angle to the surface. 

 A fine example of this is seen in 

 Onosma montana. 



Among the Compositae a very strik- 

 ing, but not a very common, form of 

 hair is what may be called serrate. 

 In its simpler variety its outline some- 

 what resembles that of wool ; but in 

 its more pronounced phase it suggests 

 the hair of some animal among 

 the rodents, particularly of the Indian 

 bat. This is the case with the leaf- 

 hairs of Hieracium tomentosum and 

 of Adenostyles lanatus. 



Glandular hairs (hairs bearing 

 glands at their extremities) are found 

 upon a large number of plants, par- 

 ticularly upon the so-called " insect- 

 ivorous " plants, and also upon many 

 others which' possess glands rather 

 for the purpose of secreting or ex- 



