52 



SEEDS AND SEEDLINGS. 



* 85. Ash.. Steep the fruits ("keys") of Ash-tree in water, then 

 cut open the fruit-cavity and notice the flat seed suspended at the 

 end of a long stalk which runs along one edge of the seed. Slice 

 away one of the flat sides of the seed and expose the straight embryo, 

 lying in the horny tissue (endosperm) filled with reserve food. 



* 86. 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 coty- 

 ledon 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 (cellu- 

 lose) is due to the secretion of a fer- 

 ment (cytase) by the cotyledon. 



* 87. 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 finally withdrawn its cotyledon 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 

 seed-coat and observe the colourless 

 end of cotyledon coiled like a watch- 

 spring 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 

 secondary roots from the base of 

 the short stem, and slit open the 



hollow sheath at its base to see the delicate pale-green plumule within. 



In older specimens the plumule has split the sheath as a result of its 



growth. 



Fig. 28. Seedling of Pine 



