746 Botanical Microtechnique 



Hedera helix is a remarkably efficient xerophyte that can with- 

 stand severe drought. However, the leaf has no striking structural 

 adaptations; its tissue organization is that of a stereotyped mesophyte. 

 This very fact makes the leaf an interesting subject for comparative 

 studies. Kill in Craf II. 



The leaf of either of the common rubber plants, Ficus elastica or 

 F. pandurata, is an interesting leathery, latex-bearing leaf. The small, 

 compact epidermal cells are overlaid by a very thick cuticle. Under 

 the upper epidermis there are two layers of large water-storage cells, 

 under which there are two layers of small, short palisade cells. Two 

 layers of compact hypodermal cells occur adjacent to the lower epi- 

 dermis. The spongy parenchyma is ver)' open and is transversed by 

 the prominent latex vessels. The latex does not seem to be preserved 

 in stainable form by FAA as well as by the chromic acid fluids. Excel- 

 lent results are obtainable with chrome-acetic 0.5-0.5 or Craf I. 



Other illustrations of lactiferous leaves are easily obtainable. The 

 leaf of the ubiquitous dandelion can be preserved in perfect condition 

 by Craf I. Leaves of the common cultivated poinsettia and of the 

 cultivated and native Euphorbias are well preserved by Craf I. These 

 leaves are not brittle and may therefore be put through an akohol- 

 xylene or acetone-xylene series. 



The succulents have very fleshy leaves that can be preserved well 

 in Craf I and dehydrated carefully in normal butyl alcohol. The 

 tissues are liighly susceptible to damage, and a procedine that pro- 

 duces severe distortion should not be condemned without a repetition 

 of the process. 



The gramineous leaf is represented by mai/e, sugar cane, sorghum, 

 foxtail, and bluegrass. Corn illustrates well the border ])arcnch\ina 

 of the vascular bundles (Fig. 13.11), but sorghum, and especially 

 sugar cane, have more striking motor cells. Bluegrass is a good repre- 

 sentative of tlu' narrow type with prominent bulUfoyni motor cells 

 along the midrib. Foxtail is intermediate between the very broad 

 and \(ry narrow types. Acceptable j)reservation can be obtained witli 

 FAA, but lor nearly perfect fixation use Craf III. Ihis procedure 

 has l)een repeated many times with corn, ^vlil1 iiniforndy good results. 

 Prior to the introduction ol ilic butyl alcohols and dioxan the older 

 midribs of corn and oilur grass leaves were dillicult to section Avithout 

 considerable breakage, but the use of these reagents has minimized 

 the diduulty. 



Monocotvledonou^. lea\c^ other than the iirainiutous l\pe shoidd 

 be induded in a comprehensive collection. The leaves of lily repre- 



