14 



THE BROAD BEAN PLANT. 



33. Micropyle. How does the water enter the seed? Is there 

 any opening in the coat ? The folds seen in the soaking seed usually 

 appear first around the edge of the seed ; this suggests that the water 

 enters somewhere on the edge. Do you recall how we found out that 

 various parts of the bean-plant contained air, which communicates with 

 the atmosphere by openings on the surface of stem and leaves ? Per- 

 haps the seed as it lost water took in air, as a piece of wood does in 

 drying. Drop some dry seeds into water that has just been boiled, and 

 notice the stream of bubbles given off. Where do the air-bubbles 

 escape ? Wipe this end of the seed dry, in some seeds that have soaked 

 for a few days, and look for the opening ; squeeze the seed and see 

 whether water oozes out. This opening is the micropyle. 



34. Seed-lobes, etc. Remove the coat from a soaked seed, starting 

 at the end opposite the scar. Note the two large whitish seed-lobes or 

 cotyledons, whose flat or slightly concave inner sides are pressed against 

 each other. When you have stripped off the upper part of the coat, 

 pull off the rest of it (the part covering the scar end) entire, like a 

 cup. Note the smooth tapering body projecting from between the 

 cotyledons and pointing towards the end of the scar where the micro- 

 pyle is ; also note the little pocket on the inner surface of the seed- 

 coat, into which the projecting body fits. 



Now pull apart the seed-lobes, and remove one by breaking across 

 the short stalk by which it is joined to the thickest part of the 

 projecting body. This brings to view a curved body lying between 

 the seed-lobes, fitting into a groove on the flat inner surface of each 



lobe, and forming a continuous line 

 with the projecting body. Has it, 

 .x^ // 1 like the latter, an even surface, or 

 ^ ' *'- does it bear any outgrowths ? 

 Examine it carefully with the lens, 

 and try to turn back the outgrowths 

 with a pin, without tearing them, 

 so as to make out the positions of 

 the outer ones. 



B n 35. The Seedling (Figs. 



5, 6). The first leaf above 

 ground consists of a single 

 piece with its margin cut by 

 shallow notches into three 

 lobes ; the second leaf is divided 



Pig. 6. Earliestfoliage-leaves of Broad deeply into three lobes, the 



middle lobe long and narrow, 

 the lateral lobes broad and 

 triangular. Then come several leaves, each consisting of 

 two stipules and a short stalk which bears a pair of oval 



Eean seedling. 



