PERMEABLE AND IMPERMEABLE SEEDS 87 



{b) The seed of Guilandina honducella absorbs no water after 

 prolonged immersion, makes no response to the changes in 

 the hygrometric state of the atmosphere, and retains its 

 weight unchanged in the course of years (p. 70). 



(3) Taking at first the seeds bared of their coats, other contrasts in 

 behaviour are brought out : — ■ 



[a) The bared kernel of Canavalia enslformh preserves its average 

 weight, but displays a greater hygroscopic variation than in 

 the case of the kernel protected by the coats (p. 71). ' 



{b) But with Guilandina honducella, when the seed is deprived of 

 its hard, shell-like covering, the kernel gains 11 or 12 per 

 cent, in weight in a few days by abstracting water from the 

 air. This increase in weight is maintained, but in a diminish- 

 ing degree, for several months, until stability is reached, when 

 the weight shows a permanent increase of 3 or 4 per cent. 

 The ultimate result is that the kernel behaves like that of a 

 permeable seed (p. 72). 



(4) The ultra-dryness of the kernel of an impermeable seed, which 

 is thus disclosed, is confirmed by the evidence supplied by the oven 

 when the seeds are exposed to a temperature of 100° C. It thus 

 appears that the amount of water regained from the air by the bared 

 seeds of Guilandina honducella represents the deficiency in its water- 

 contents, as compared with the bared seeds of the permeable type 

 belonging to Canavalia ensiformis (p. 73). 



(5) The next curious feature in impermeable seeds here brought to 

 light is the fact that the shell-like covering of the seed of Guilandina 

 honducella has the same quality of ultra-dryness, though in a somewhat 

 diminished degree, and the same capacity of supplying this deficiency 

 by absorbing water from the air, the larger water-percentage of the 

 shell being associated with a diminished absorptive capacity of the 

 freshly exposed material. On the other hand, the coats of a seed of 

 Canavalia ensiformis behave like the kernel, maintaining the same 

 average weight when removed from the seed, but subject also to 

 ordinary hygroscopic variation (p. 75). 



(6) The same effects are produced by puncturing or filing the 

 impermeable seeds of Guilandina honducella, though the increase in 

 weight is far more gradual and is extended over months. This 

 behaviour is contrasted with that of the permeable seeds of Canavalia 

 ensiformis, where the effect of puncturing the coats is merely to increase 

 somewhat the normal hygroscopic variation of the weight (p. 76). 



(7) As first accidentally disclosed and subsequently more fuHy 

 investigated, it is shown that exposure to a temperature of 100° C. 

 but slightly affects the capacity of the seeds of Guilandina honducella 

 (whether in the case of bared kernels or detached shells) of adding to 



