HYGROSCOPICITY 171 



the swelling that precedes germination, and that the increase Thehygro- 

 in the water-contents due to hygroscopicity is quite insufficient Iction does 

 for the purpose. The question whether, under ordinary g°r^^ation 

 conditions, seeds wiU take up sufficient water from the air for 

 germination he answers in the negative ; but he considers that 

 germination would be likely to occur when through frequent 

 great changes of temperature, condensation takes place on the 

 surface of the seed. In the extreme conditions reproduced in 

 his experiments, when seeds of Flax and of the Kohl-rabi were 

 exposed for many days to air saturated with moisture, he found 

 that an increase in weight of 22 or 23 per cent, did not lead to 

 germination. In such experiments germination would occur 

 only when, through condensation within the vessel, liquid water 

 comes into contact with the seeds. 



Jodin put the distinction between the increase of water due 

 to hygroscopicity and the amount of water required for ger- 

 mination very clearly in the case of peas. He shows that 

 whilst the minimum amount of water required to be absorbed 

 for germination amounts to 67 per cent, of the weight of the 

 resting seed, the greatest increase in weight involved in the 

 hygroscopic range of peas is not more than 23 per cent., a 

 quantity he characterises as insufficient to provoke germination. The ger- 

 Although he found that the water of hygroscopicity was quite ™o^^*nes 

 insufficient to produce germination, the results of one of his wroJJo ic 

 experiments described in Note 4 of the Appendix might have maximum 

 been interpreted in this sense by a superficial observer. In thesatura- 

 order to ascertain the minimum amount of water requisite for *i°"'i™t- 

 germination, he placed the peas on a platinum support suspended 

 in moist air, the metal condensing the aqueous vapour in fine 

 drops and communicating the liquid water to the peas. It is 

 evident from Jodin's experiments that, as far as the water- 

 contents of the seed are concerned, the germination point lies 

 between the maximum of the hygroscopic range and the limit 

 of the seed's capacity for absorbing liquid water, or, in other 

 words, between the hygrometric extreme and the saturation 

 point. 



