290 MacMillax: Observations on Nereocvstis 



run length- 



fcrence between young lamina and stipe is the early development 

 in the former of mucrlage canals which lie in rows just within the 

 epidermis. , The cortex I'n this .stage consists .of. about twoJayers 

 of cells, those just under the epidermis being generally larger than 

 the ones which abut upon the plate of cells regarded here as cen- 

 tral cylinder. The secretion ceils of mucilage ducts in this ma- 

 terial seem to line the canal not only along the inner side but 

 along the outer as well. They stain deeply with aniline-water- 

 safranin. The cells of the central plate are narrow, much thicker- 

 walled than those of the pith-web in the stipe and packed together 

 in such a way as to leave only very small intercellular spaces. 

 Many of them run crosswise of the leaf while others 

 wise. The result of this is to make this area not dissimilar to the 

 same area in longitudinal section, but as the leaf matures the pith- 

 web character of the middle lamella becomes more marked and 

 trumpet-hyphae are present in longitudinal sections of the lamina 

 of a 1 2 cm. plant. In a leaf of this size the cortex consists of five 

 or six layers of cells, the inner larger than the outer, but along the 

 niiddle lamella the cortical cells arc smaller and elongated in the 

 axis of the leaf Where they abut on the middle lamella they pass 

 over Into the character of pith-web tissue. B}' the time the leaf 

 has acquired this size the secretion-cells of the mucilage ducts have 

 for the most part broken down .and cryptostomata have developed 

 in the furrows which lay over the mucilage ducts of the younger 

 leaf. The epidermal cells in young leaves are about three times as 



f 



broad as they are high, are denscl)' protoplasmic and stain vividly. 

 Interesting rows of short cylindrical cells are found in the 'pith- 

 web, their diameter sometimes exceeding their height. Such cells 



" I 



finally become elongated into the .ordinary hyphac of the web. 

 Cross sections of the leaf of a 1 2 centimeter plant show some sieve- 

 tubes still present and more abundant In the s^rowine region of the 

 .- .leaf which is essentially basal. 



. Towards the tip of the leaf the lamina Is thinner in the 1 2 cm. 



,, material, the epidermal cells are more nearl)- square in outline, the 



^ ^ cortical cells are very large and appro.ximately isodiametrical, while 



,,,,.the central lamella is reduced to about two layers of thick-walled 



cells of elongated shape with few intercellular spaces. From this 



region mucilage ducts and sieve-tubes are absent for.it was formed 



