GERMINATION, GROWTH, TISSUE TENSION. 185 



172. Broad Bean Seed. Examine (1) dry seeds; 



(2) seeds that have been soaked in water for two days ; 



(3) pods of different ages, containing fresh seeds in different 

 stages of development. 



(a) Note the shape of the ripe seed. At the thicker end 

 there is a black or brown mark (hiliim) obviously the 

 scar formed when the seed became detached from the stalk 

 which fixed it to the inside of the pod. 



(fe) Examine from time to time dry seeds that have been 

 placed in water. At first the surface is thrown into folds 

 evidently the coat at first absorbs water and swells more 

 rapidly than the seed- contents, hence it becomes loosened 

 and is* easier to remove in a well soaked seed. The wrink- 

 ling of the coat is very marked in Phaseolus (Scarlet 

 Runner and French or Haricot Bean). 



(c) Drop some dry seeds into very hot water, or fix 

 some seeds into a spirally coiled piece of copper wire and 

 put this in a beaker of water boiling over a Bunsen, and 

 note the air-bubbles that escape from near the hilum. 

 Wipe dry the hilum end of a soaked seed, and squeeze the 

 seed water oozes out of a small slit-like pore (micropyle) 

 at one end of the scar. The micropyle is very conspicuous 

 in Phaseolus, having a raised margin. 



(d) Remove the coat from a soaked seed, starting at the 

 end opposite the scar. Note the two large whitish coty- 

 ledons, whose slightly concave inner sides are pressed 

 against each other. After stripping off the upper half of 

 the coat, pull off the rest of it (the part covering the scar 

 end) entire like a cup. Note the smooth tapering radicle, 

 projecting from between the cotyledons and pointing 

 towards the micropyle end of the hilum ; also note the 

 little pocket on the inner side of the seed-coat, into which 

 the radicle fits. 



(e) Pull apart the cotyledons, and remove one by break- 

 ing across the short stalk by which it is joined to the 

 thickest part of the radicle. Note the curved plumule, 

 lying between the cotyledons, fitting into a groove on the 

 inner surface of each cotyledon, and forming a continuous 

 curved line with the radicle. Examine the plumule care- 



