130 HISTOLOGY OF ANGIOSPERM STEM, ROOT, ETC. 



D. 



moisten the preparation with alcohol, to remove air, and 

 mount in glycerine ; to make the tissues more transparent, 

 heat the sections in the glycerine, since clearing reagents 

 like potash obscure the dense granular contents by which 

 the pollen-tubes are recognisable. 



Pick the pistil from a faded Chiokweed flower, mount, and note 

 (1) the ovary wall with three vascular bundles ; (2) the three curved 

 styles, with stigmatic hairs on their convex sides ; (3) the yellow 

 pollen-grains held between the stigmatic hairs ; (4) the pollen-tubes 

 passing from the grains into the tissue of the style. Examine faded 

 flowers of different ages, and look for ovules with a pollen-tube 



applied to the micropyle. 



Similar observations may be 

 made on many other plants. 

 For the passage of the pollen- 

 tubes down the central canal 

 or the central conducting 

 tissue of the style, examine 

 longitudinal sections of stig- 

 ma and style of Foxglove, 

 Rhododendron, etc. 



The entrance of the pollen- 

 tube into the micropyle of the 

 ovule is easily seen in faded 

 flowers of Speedwell, Chick- 

 weed, Shepherd's Purse, etc. 

 Treat the teased-out ovules 

 with chloral hydrate or car- 

 bolic acid to make them trans- 

 parent. 



EMBRY 



VASCULAR BUNDLE 

 IN SEED-STALK 



Root. 



Fig. 34. Development of Embryo in 



Shepherd's Purse. 



A, young seed (treated with caustic potash) 

 showing embryo at micropyle 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. 



In ovules mounted entire in 

 teguments, micropyle (a pollen' 

 this), and curved embryo-sac of 



167. Development of 

 Embryo (Fig. 34). This 

 is very easily studied in 

 the Shepherd's Purse. 

 Remove the fertilised 

 ovules from fresh ovaries 

 3 to 6 mm. long, and study 



(a) the embryo in situ, 



(b) isolated embryos, in 

 ovaries of different ages. 



potash note the stalk, in- 

 tube may be seen entering 

 the campylotropous ovule ; 



