178 Botanical Microtechnique 



be extracted. Soak the kernel in a solution that is based on the 

 steeping liquor of corn processing j^lants. The solution used at 

 present contains 2% sodium sulfite and 2[', lactic acid. It is necessary 

 to test the time and temperature factors with each lot of grain. Try 

 20° and 35°C., and intervals of 1 to 3 days. When the germ can be 

 loosened easily, trim away unessential parts of the germ, subdivide 

 if desired, and drop into the fixing fluid. 



Small kernels, up to 10 days after pollination, are well fixed in 

 Craf I or II. Older kernels and extracted embryos are penetrated 

 better by Craf III. Xylene is the poorest solvent for infiltration, and 

 chloroform is satisfactory only to the 15th day. Thereafter, a dioxan- 

 normal or dioxan-tertiary butyl alcohol series makes possible the 

 sectioning of 40-day kernels in paraffin (Sass 1945) . (See frontis- 

 piece) . 



Embedded kernels must be soaked in warm water before section- 

 ing. Adhesion of sections to the slide requires careful flattening of 

 the ribbon, without overheating. For some research problems, hema- 

 lum alone permits adequate diagnostic observation. A safranin-fast 

 green stain is attractive, and for exhibition purposes it is possible to 

 make gaudy muhiple stain preparations. Ages of kernels are given 

 in the legends of figtnx' 15.8. 



Capsella bursa-pastoris is a favorite subject for embryology. The 

 siliques are soft and easy to section. Although the seeds lie in the 

 locules at various angles, seeds are so abundant that almost every 

 section has complete embryos. Remove the fruits from the inflores- 

 cence, and classify them roughly into age groiqxs in accordance with 

 their distance from full-blown (lowers. Process each class in a separate 

 bottle. A sequence of stages in embryo development can be built up 

 bv sectioning fruits from the se\eral lots. Trim two sides of the silicpie 

 to piomotc penetration. The long sili(|ue of Mdllhiola also max be 

 used. Divide transversely into 2- to 3-nun. lengths for killing, and 

 cut microtoine sedions longitudinally. Use Craf I for either of these 

 criicifers. 



Lycojjcr.slf inn <'S( iiJoil iini . tlie tomato, is an cxcelU'iit subject lor 

 dicot embryology. Use the small currant tomato, L. piiiipiiicllifoliiiui, 

 seeds of which are obtainable from seed dealers. Slides of fertiliza- 

 tion and the very young embryo are dilTicult and time-consuming 



Fio. 15.8— Zrn mays: n, kernel of pop corn 10 days after pollinalion; h. enibrvo of 



(Itnt (oui, 10 davs; c. cinhiAo. 15 davs: d. transverse section of kernel of dent corn, 



25 da\s: r. kernil ot pop iomi. "20 da\s. 



