744 Botanical Microtechnique 



with Craf II and TBA dehydration. The latter reagent minimizes the 

 brittleness of these subjects. A disadvantage of the rosaceous leaf is 

 the presence of excessive brown pigmentation in the cell walls and 

 masses of yellow gummy materials in the cells. The embedded pieces 

 of leaf in the paraffin block are decidedly dark, and the staining 

 effects tend to be muddy, especially with the hematoxylins. The use 

 of a safranin-fast green or safranin-aniline blue combination makes 

 slides with fairly clean color contrasts. Lilac and privet leaves can 

 be processed by the above methods. Many other trees and shrubs have 

 leaves in this firm-textured category. Geranium leaf is firm and easy 

 to process. Craf V gives excellent results. Do not use pieces with large 

 veins unless TBA is used for dehydration. 



Leaves of softer character than the foregoing are illustrated by 

 various easily obtainable legumes. Kidney bean, soybean, clovers, and 

 alfalfa have more or less pubescent leaves; peas and horse bean have 

 practically glabrous leaves. All of these leaves have been killed success- 

 fully in FAA, but failure occurs often enough to justify more critical 

 methods. Excellent preservation of alfalfa and soybean leaf has been 

 obtained with Craf III followed by an acetone- T5/J series (Fig. 11.1) . 

 The thinness of the cell walls requires a stain of good contrast, such 

 as hemalum, followed by safranin, the xylem stain. The coal-tar dye 

 counterstains are likely to yield weakly stained parenchyma and barely 

 visible plastids. 



1 he leaves of the Solanaceae and Cucurbitaceae represent the very 

 tender type of broad leaf. Subdividing of fresh leaves must be done 

 with the greatest care because of the open and fragile construction 

 of the parenchyma. The glandular hairs should also be preserved 

 intact. 1 he best killing is obtained with a mild fluid, such as Craf I. 

 Practically perfect preservation of tobacco leaf has been obtained 

 consistently with this fluid. Although the blade is soft in lea\es of this 

 type, the veins are large and firm, justifying the use of TBA. 



Begonia leaf is an interesting tender leaf. I'he epidermal cells on 

 both sides are enormous, the two layers occupying more than two- 

 thirds of the thickness of ihe leaf. Ihe narro\v interior layer consists 

 of poorly defined palisade and extremely loose spongy parenchyma. 

 All these interior cells contain chlor()j)hyll; each cell has relati\ely 

 few, but very large chlor()j)lasis. A leaf of this type is obviously 

 difficult to preserve. Good killing lias been obtained with chrome- 

 acetic 0.5-0.5, washed by diffusion in a large volume of water, 

 followed by the ethyl alcohol-xylene series. Cut 15 ^i thick in order to 

 keep the large epidermal cells intact. Coleus is another common 



