216 



FLOWERS AND THEIR WORK. 



D. 



EMBRY 



In each ovule a cell, the egg, is produced. When the 

 flower has opened the stigma becomes wet and sticky, so 



that pollen-grains are held 

 on it. Each pollen-grain 

 grows into a long fine tube 

 which burrows down through 

 the style and eventually 

 enters the little opening 

 in the ovule and its 

 tip touches the egg-cell, 

 which lies close to this 

 opening, embedded in the 

 ovule (Figs. 69-71). The 

 pollen-tube opens, and 

 a male cell passes from it 

 to the egg-cell and fertilises 

 it, i.e. fuses with it. Then 

 the fertilised egg develops 

 into the young plant (em- 

 bryo) ; the part just outside 

 of the embryo also grows 

 to produce the endosperm, 

 which may or may not be 

 absorbed by the embryo be- 



VASCULAR BUNDLE 

 IN SEED-STALK 



Root 



Fig. 71. Development of Embryo in 

 Shepherd's Pui-se. 



A, Young Seed (treated with caustic potash) 

 allowing Embryo at rnicropyle-end of 

 curved Embryo-sac; m., Micropyle; 

 B-F, stages in growth of Embryo ; G.P., 

 Growing- point of Stem; Susp., Sus- 

 pensor; b.c., Basal Cell ; Cot., Cotyle- 

 don ; Em., Embryo. 



fore the seed ripens, the seed 

 being non-endospermic ("ex- 

 albuminous") in the former 

 case, endospermic (" albu- 

 minous ") in the latter. 



(a) Examine the stigma of a Tulip (or other flower with large stigma), 

 and see whether it is wet. If so, shake over it some powder, e.g. flour 

 or chalk, and then try to blow the powder off. Place a stigma on 

 your tongue, and see whether it is sweet. Place a few stigmas in some 

 Fehling's solution in a test-tube, and heat (test for sugar). 



(6) Place some water in watch-glasses and add different amounts of 

 sugar, so as to get solutions varying in strength from 5 to 20 per cent. 

 Into each place some pollen ; try various plants. In the case of the 

 Broad Bean and the Sweet Pea a 10 per cent, solution is about right, 

 and in an hour, or even less, you will see a slender thread growing 

 from some of the grains ; this is the pollen-tube, which resembles a 

 root-hair in appearance (Fig. 69, D). If you have a microscope, fix 

 a ring of cardboard or of plasticine on a glass slide ; put a drop of 



