220 PKACTICAL BOTANY 



while the other side is almost smooth : about two-thirds 

 down the smooth side a small circular depression will be 

 seen : this indicates the position of the embryo. 



Cut the seed transversely so as to traverse the 

 embryo, and observe the external brown seed-coat, 

 which closely invests the hard pearly mass of endo- 

 sperm, in which is embedded the relatively very small 

 embryo. 



RESERVE AND TRANSITORY MATERIALS IN SEEDS, 

 TUBERS, &C. 



I. Starch from the potato tuber has already been 

 described with its reactions on p. 44 47 : as further 

 examples of its occurrence in seeds, cut sections of the 

 cotyledon of the Pea or Bean : stain with iodine solution, 

 and observe the large, oval starch-grains distributed 

 through the tissue : note at the same time the proto- 

 plasmic matrix, and numerous small aleurone grains, 

 which are stained yellow or brown. 



Cut sections also of the endosperm of the Maize, and 

 treat with solution of iodine. Note the polygonal 

 starch-grains (blue), and the protoplasmic matrix 

 (brown). 



Leukoplasts, or Starch-forming Corpuscles, These are to 



be found in colourless tissues, in which a storage of starch is taking 

 place ; e.g. a young Potato, the rhizome of Iris, or Canna, &c. 



Cut up very young Potatoes into small pieces, and treat with 

 picric acid : wash out carefully with dilute alcohol, and harden. 



Cut sections parallel to the surface, and not far below it (since 

 the leukoplasts are best seen in the most superficial cells im- 

 mediately within the corky rind) : treat the sections for a few 

 minutes in alcohol with a few drops of iodine solution added ; or 



