142 GERMINATION, GROWTH, TISSUE TENSION. 



181. Date. Examine a Date seed (i.e. the "stone"). Notice 

 the deep groove along one side. Scrape the surface on the other 

 side, to see the small embryo embedded in the stone (endosperm). 

 Cut the stone across at this point ; then dip the stone in dilute 

 sulphuric acid and apply iodine (test for cellulose). Plant some 

 Date stones in damp sawdust or soil, set in a warm place (a heated 

 greenhouse, if possible), and sketch stages in their germination. 

 Open the stone in some of the seedlings, and then notice the 

 softening of the stone and the extent to which the cotyledon has 

 grown inside it. Notice in sections of the stone that the cell- walls 

 become thinner, and that starch appears in the young root and 

 shoot, in darkness as well as in light. The digestion (conversion 

 into sugar) of the reserve food (cellulose) is due to the secretion of a 

 ferment (cytase) by the cotyledon. 



182. Onion. Examine a seedling of Onion before the 

 embryo has finally withdrawn its cotyledon from the seed. 



Observe (a) the long slender root, (b) the slight swelling 

 at the base of the root marking the position of the 

 relatively short stem from which arises (c) the long, hollow 

 cotyledon whose tip is still within the seed-coat. 



Remove the testa and observe the colourless end of 

 cotyledon coiled like a watch-spring as it lies within the 

 seed. During germination the cotyledon absorbed the 

 food from the endosperm and passed it on to the growing 

 parts. 



In older specimens observe how the air-exposed tip of 

 the cotyledon withers ; also note the formation of secon- 

 dary roots from the base of the short stem. Slit open the 

 hollow leaf-sheath at its base and discover the delicate 

 pale- green plumule within. In still older specimens the 

 plumule itself has split the sheath as a result of its growth 

 and development. 



II. SOME EXPERIMENTS ON GERMINATION. 



183. Water present in "air-dry" Seeds. (a) Are 



the " dry " seeds sold by the seedsman quite dry, or do they 

 contain any water at all ? Into a dry test-tube (warm 

 the tube all over to make sure it is quite dry) put a few 

 " dry " Peas or Beans and heat over a Bunsen or spirit 

 lamp, applying the flame to the bottom of the test-tube. 



