1!-. 

 ondar;; c^aials tiir.s formed is alv/r.ys small, fex.'er than of 

 the primary ones, but there is apparent!, ■ no regularity 

 either in nimiber or position. 



Wlien the epidermal layer of a section has divided by 

 one longitudinal anticline and three transverse ones (Fig. 

 27), foiming thus eight cells allogetlier, four in the 

 length of a se,'^^ent and tv.'o in the width of a section, 

 there is cut from each of these cells, by a circular tinti- 

 cline at tlie acroscopic end, a small cell v/hich gives rise 

 to one of the numerous trichomes that clothe the yonnr 

 leaf. Th.e rest of the original epidermal cell then divides 

 to four cells ".vitli the trichome at the acroscopic end of 

 one of the upper pair (Fig. 23), then furth.er divisions 

 follow Lmd at maturity the epidermal cells become much 

 elongated (Fig. 29), as has been shov/n by Russov/ (*72) and 

 also by Meunier for Pilularia, v/hile some of them ma^^ later 

 form more secondary trichomes. Each trichomo cell grov/s 

 out beyond tlie surface of the epidermis (Fig. 2C) cjid 

 swells at its outer end to a knob, which soon elongates, 

 in the direction of the lengt-h of the petiole* On the 

 basiscopic side it projects but slightly, while it grows 

 out toward the tip of tlie leaf into th.e long multicellular 

 hair, v/hich is supported by the basal or stalk cell that 

 remains v/edged in between the other epidermal cells (Fir. 

 30). Before tlie leaf reachijs maturity these hairs separate 



