136 GERMINATION, GROWTH, TISSUE TENSION. 



fully with a lens, and with a pin turn back the minute 

 foliage-leaves which it bears. 



(/) Make sketches, at least twice the natural size, of 



(1) the entire soaked Broad Bean seed, from the scar end ; 



(2) same from the front i.e. thicker edge showing the 

 micropyle and the bulge caused by the radicle ; (3) same 

 in side view ; (4) side, and (5) front views of embryo after 

 removing seed-coat ; (6) scar end portion of empty seed- 

 coat, showing the pocket into which the radicle fits ; 

 (7) side, and (8) front views of embryo with one cotyledon 

 broken off ; (9) section of whole seed, cut between the 

 cotyledons, to show pocket with radicle fitting into it. 



173. Stages in Germination. Study and sketch 

 various stages in the germination of Broad Bean. Note 

 (1) that the radicle emerges from the seed in advance of 

 the plumule ; (2) that there is a V-shaped split in the coat 

 along the edge of the radicle-pocket this is caused by the 

 root swelling and raising the outer wall of the pocket as a 

 triangular flap, the apex of the triangle not reaching the 

 micropyle ; (3) that in whatever position the seed has been 

 planted, the radicle grows downwards and the shoot up- 

 wards curving, if necessary, in order to take the vertical 

 direction. 



Note also (4) that the stalk of each cotyledon lengthens, 

 pushing the cotyledons apart and helping the plumule to 

 emerge from between them ; (5) that the plumule remains 

 for a time strongly hooked at the top, but gradually 

 straightens out as it grows upwards ; (6) that the coty- 

 ledons remain in their original position, covered by the torn 

 seed-coat, and gradually shrivel as germination proceeds ; 

 (7) that the bud in the axil of each cotyledon may grow 

 out to form a leafy branch, especially if the plumule itself 

 has been injured ; (8) that roots may grow out from the 

 base of the plumule, especially if the radicle has been 

 injured. 



174. Seeds and Seedlings of Fhaseolus and Pisum. 

 Examine seeds and seedlings of French Bean (Phaseoltis vulgaris) 

 and Scarlet Runner (Phaseolus multiflorus). In both note the 

 position of the hilum, the conspicuous micropyle, the wrinkling of 



