n. 



vides hy anticlines luiu periclinos to lorra t.]ie mesoplr;!! 

 cells of tlie pia+'Ure le;\f ( mp.^Firrr;, l^"- - 19 ), v/liile tlie 

 outer cell /];ives rise to both the lonratudino.l and the 

 transverse pertitions "between tlie air ctmal"? (p.c, Fi-^s. 

 15, 1^), T]iese latter cells swell out in the middle (Fi.-^s. 

 lo - 18) tmd grov/ out : t the eiids into papilla like tips, 

 wliich are in contact v/itli th.ose of th^eir fellows of th.e 

 adjacent sections (Fir;s. 17, 21), leavin^^ Ein intercellular 

 space "betv/ecn tiiese rmd tlie mesophyll cells and also one 

 above and belov' each papilla, coimectin,^ this v;itli the 

 prinary air canal fenced hetv/een the partition cells and 

 the hypodermis (Firs. 1'^, 17, 21). These papillae are soon 

 cut off by lorigitudinal anticlines (Figs. 17, 21 - 23), and 

 thus is fonned a pair of small nearly isodiametric cells, 

 in each canal opposite each of the primary partition cells, 

 of which there are usually eight in the lengLh of a seg- 

 ment. From these eight pairs of cells, one cell in each 

 pair being from eacli of the opposite primary partition 

 cells bordering on an air canal, are developed the eight 

 transverse partitions of tlie air canal in each setTnent. 

 These remain one cell thick even till maturity, but later 

 in their development many intercellular openii\gs or pores 

 are formed, allowing the passage of ai^^ throurh tliem. (c.r.' •» 

 Figs. 1^, 20, 24). Except for tliese pores, the partitions 

 of the mature leaf stretcJi completely across from meso- 



