212 SECRETION AND EXCRETION 



5. With a sharp knife cut germinating date seeds cross- 

 wise into slices about 2 mm. thick and put them through the 

 process of fixing, hardening, and imbedding in paraffin, and 

 sectioning, described in Chapter XV. When it comes to 

 staining the sections place the slide on which they are mounted, 

 after the paraffin has been dissolved away in xylene and the 

 xylene rinsed off with alcohol, in a dish of safranin (page 326) 

 for a few hours, and then rinse out the surplus safranin in water, 

 dehydrate quickly in 95 per cent, alcohol, rinse in xylene and 

 mount in balsam. Study the epidermis of the enlarged coty- 

 ledon. These cells secrete enzymes for the digestion of the 

 endosperm exterior to them. Draw a few of the secreting 

 cells together with the adjoining cells of the cotyledon and 

 endosperm, and by stippling indicate how the secreting cells 

 differ in appearance from the others. 



6. Soak grains of Indian corn over night and cut the thin- 

 nest possible free-hand sections across the embryo and endo- 

 sperm. Mount the sections in dilute glycerine. Compare the 

 appearance of the epidermis of the cotyledon with that of the 

 date. These cells of the corn are also enzyme-secreting. 



7. Scrape hairs from the surface of Pelargonium zonale or 

 other plant bearing glandular hairs, mount them in a drop 

 of dilute glycerine and study them under high magnification. 

 Draw some of the glandular hairs. 



8. Study longitudinal sections of the stem of some milk- 

 weed or of the greenhouse Euphorbia splendens for laticifer- 

 ous vessels. Make a drawing showing the branching and 

 anastomosing habit of these vessels. Treat the section with 

 iodine. Are there indications of starch and proteids? 



9. Cut cross-sections through the cotyledons of acorns; 

 examine them in water and allow a dilute solution of chloride 

 of iron to run under the coverglass (see under Tannins in Chap- 

 ter XVII). Note the indication of tannin in some of the cells. 



10. Cut cross-sections of the seed of Strychnos nux- vomica 

 and test them for alkaloids as described under Alkaloids in 

 Chapter XVII. 



