FORM OF THE PLANT-CELL. 



77 



developed, but further special researches are needed. Frequently a hair 

 consisting of a single cell is developed into manifold forms, sometimes 

 swelling into a knot (figs. 88, 89.); at other times forming numerous 

 branches (fig. 90.), as, for instance, in the hairs of some species of 

 Malpighia and Rhamnus, in which the branches of the hair extend in 

 two opposite directions, and are pressed flat upon the surface of the 

 epidermis ; and also in the remarkable four-armed pair of cells in 

 the vessels of Utricularia. These at first consist of two round cells 

 lying close to one another; they then form two short pedicels, which 

 swell and form a little head, each of which sends out two arms, a long 

 one and a short one. 



In most cases, several cells go to form a hair. In this case the 

 branches often consist of cells (fig. 91.). Amongst compound hairs those 

 bearing knobs are very frequent. The pedicel either consists of a 

 single cell, or a row of cells (fig. 92. b\ or several cells. The same 



thing occurs in the structure of the knob, which is often green, or 

 coloured, or contains a peculiar secretion.* Sometimes hairs exhibit 

 in the interior spiral vessels, as in Drosera. The most remarkable 



* I cannot entertain the notion of a gland in the vegetable kingdom ; so that here, as 

 elsewhere, I make no distinction. 



9i Lateral view of a portion of the epidermis of the Wigandia wrens, with two hairs : 

 a is a stinging hair, with a knob, and circulating fluid in the interior ; 6, a club-shaped 

 glandular hair. Every one of the simple cylindrical cells, which, placed one upon the 

 other, form the stalk, exhibit a cytoblast and circulation. The knob, formed out of 

 many little cells, is covered with secreted resin. The arrows show the direction of the 

 streams. 



93 A prickle-hair from the leaf of Dipsacut fullonum. It consists of a long, some- 

 what bent cell, thickened by layers (a), which is embraced at the base by an elevated 

 mass of porous epidermis-cells. 



