find i\t maturity mim-j small intGrcolliilar openin.^s or pores 

 thn 'neats* of Hoimior, wiiicli allov: comniLnication betv/ecn 

 adjacent CLmala (L.p.p., Ft^s, 19, '10, :'J:)» 



In the type of petiole v/ith five sections in eacli 

 segment, there are, as v;e have seen, fourteen primary air 

 canals. IVlien the segments of "both sides of the petiole form 

 only foiir section, v/alls, there are but tv/elve canals, 

 v/hile v;]ien, as occasionally liappens, one side foirns four 

 and the other five sections, v/e find thirteen canals. All 

 tliree types are foi^nd in tlie older petioles, hut it ic intc 

 esting to note that the only figure of a crocs section of 

 a petiole that I have seen, that of Bischoff (*28), is a 

 petiole of the^ frequent type v/ith thirteen canals. 



At a comparatively late stage of the development of 

 the leaf, v/h.en tlie longi-tudinal partition is already many 



cells "broad ra.dially, the outer cells, next to the h.ypo- 

 dermis, or tlie iriner ones next to the nesophyll cells, may 



spli'. by a longitudinal anticline. The daiigliter cells then 

 separate laterally (a.c.^Fifr. I ^), and divide "by periclinos, 

 forming thus a nev/ canal bordered by these cells and the 

 hypoderais or tliese tmd tlie mesophyll cells. Tliis splitting 

 of the primary partition may apparently proceed through its 

 wliole radial width, ind thus f or ■ a secondary canal hc- 

 tweon the tv/o layers, haij:ly to "be distinguished from , ho 

 primar;^ canals in the mature leaf. The number of tJie sec- 



