70 STUDIES IN SEEDS AND FRUITS 



(")^''e- On placing these two seeds in water we obtain very 



permeability, different results. That of Guilandina bonducella absorbs no 

 water and preserves its original weight after an immersion 

 of many months or even years. On the other hand, the 

 seed of Canavalia ensiformis begins to swell in a few hours, 

 and within twenty-four hours has doubled its weight. One 

 seed, therefore, is impermeable or waterproof, whilst the 

 other is permeable. But this difference in behaviour is 

 associated with a difference in other qualities. If we 

 weigh the seeds daily for a week or two, employing a 

 quartz pebble as a standard of comparison, we observe 

 that the seed of Guilandina bonducella behaves exactly like 

 the pebble and keeps its weight to within a small fraction 

 of a grain. The seed of Canavalia ensiformis^ on the con- 

 j6)asre- trary, varies considerably in response to the daily changes 

 pgro- ^" '^^ the atmospheric humidity, the amplitude of Its variations 

 popicity. amounting to 2 or 3 per cent, of its average weight. One 

 seed, therefore, behaves hygroscopically, and the other does 

 not. As might have been expected, it is the impermeable 

 seed of Guilandina bonducella that is non-hygroscopic, whilst 

 with the seed of Canavalia ensiformis permeability and 

 hygroscopicity go together. When extending the weighing 

 observations over twelve months, we find the same features 

 of difference displayed. Whilst the Guilandina seed maintains 

 its weight unchanged, the Canavalia seed continues to exhibit 

 the same hygroscopic variations. If we were to represent 

 these results in a diagram, we should denote the behaviour of 

 the seed of Canavalia ensiformis and that of the Guilandina 

 seed by a horizontal line. The line of the last named 

 would be even, but that of the Canavalia seed would 

 display numerous zig-zag irregularities, marking the hygro- 

 scopic responses of the seed. It is essential to understand 

 that we are here dealing with seeds that have completed 

 their spontaneous drying in air. Where the shrinking 

 and drying process is unfinished quite other influences 

 come into play. 



