214 STUDIES IN SEEDS AND FRUITS 



We see here that whilst with the coats the differences in 

 the swelUng ratios and water-percentages of all three types of 

 seeds are small, the differences that do exist are in accord with 

 the principles laid down in Chapters IV. and VI. Thus, the 

 coats of permeable seeds have a smaller swelling ratio and a 

 larger water-percentage than the coats of seeds that are more 

 or less impermeable. But the difference is small, and it is to 

 the kernels, where the contrast between the three types of 

 seeds is pronounced, that we chiefly look for evidence in this 

 direction. The determination of the amount of the swelling 

 ratio by the quantity of water held by the seed is fully 

 established by the behaviour of the kernels, the kernel of an 

 impermeable seed holding on the average not much more than 

 half the water held by the kernel of an average permeable 

 seed, and possessing a much larger swelling ratio. In the 

 first we have a water-percentage of 8*3, associated with a 

 swelling ratio of 2*6 1. In the second the water-percentage 

 amounts to I4'9, and the swelling ratio to 2*04. 



The effect of oil on the absorption of water by the kernels 

 absorption of of the seeds preparing for germination is another point to be 

 referred to. The effect is shown in the small swelling ratio of 

 such kernels, a fact indicating a relatively small absorption of 

 water. Such seeds have a regime of their own when swelling 

 for germination. Ordinary permeable resting seeds, like those 

 of Canava/ia, Faba^ Pisum, and Phaseolus^ dealt with in the 

 tabulated summary given above, display an average swelling 

 ratio for the kernel of 2*04, taking the weight of the kernel of 

 the resting seed as i. But permeable seeds with more or 

 less oily kernels exhibit a much smaller swelling ratio. Thus, 

 the kernels of the seeds of Hura crepitans, Anona muricata, and 

 Luffa acutangula possess sweUing ratios of i-68, 1*57, and 1-49 

 respectively ; whilst with Ricinus communis the swelling ratio 

 for the entire seed is only i'33, as against 2*04 for typical 

 entire permeable seeds belonging to the four leguminous 

 genera above named. It will thus be seen that whilst an 

 ordinary permeable leguminous seed doubles its weight by 



