42 STUDIES IN SEEDS AND FRUITS 



and the Cruciferae, where the seeds possess swelling ratios quite 

 as low as those of baccate fruits, and to these groups may be 

 added often plants with capsular fruits. There would, there- 

 fore, seem to be some common influence that brings not only 

 the seed of the berry, but the seed of the cruciferous pod, of 

 the capsule, and of dry-looking indehiscent fruits, into contrast 

 with the seed of the legume. 

 An appeal to We will now appeal to the varying behaviour of seeds 

 deviations in within the limits of a species, with the hope of discerning in 

 capadty of^ their differences some clue to the origin of the greater contrasts 

 j seeds of the between the seeds of plants that stand apart from each other. 

 We have before seen that the ordinary range of the swelling 

 ratios in the same plant is small ; and inquiry has led me to 

 believe that we shall not profit much by the study of small 

 differences. At times, however, there are deviations that lie 

 quite outside the usual range of the swelling ratios. The 

 cases of excessive swelling, which are probably just as apt to 

 occur in nature as they are in our experiments, are often readily 

 explained by the unusual prolongation of the swelling period 

 in normal seeds, which allows the seed to take up more water 

 than is actually needed. Both permeable and impermeable 

 seeds are liable at times to absorb much more freely than is 

 usual. Under such conditions germination usually fails ; but 

 occasionally it takes place, and we obtain swelling ratios far 

 in excess of the average. Then, again, we have cases of 

 excessive swelling, also ending at times in germination, where 

 there has been abnormal shrinking in the drying of the moist 

 pre-resting seed ; and since the exceptional loss of water has 

 to be made up in the preparation for germination, accord- 

 ing to the compensatory relation between the shrinking and 

 swelling processes before established, we find this expressed 

 in the increase of the swelling ratio. In these cases we are 

 concerned only with permeable seeds, as will be explained in 

 a later page. 



On the other hand, we have instances of swelling ratios con- 

 siderably below the average and equally outside the ordinary 



