VITALITY AND GEBMINATION OF SEEDS. 223 



over Wheat is due to the fact, that the Wheat grains are 

 covered simply by a thin membrane., which was originally 

 the wall of the ovary, whilst the Barley has in addition to 

 this an external membranous or rather scaly covering, 

 formed by the adherent Palea. The fact that Barley 

 survives longer than Linseed does shows that the mem- 

 branous covering of the former is less readily penetrated 

 by alcohol than the mucilaginous covering of the latter. 

 A comparison of Peas with Cress or Linseed gives the 

 same result. Hence we conclude that membranous or 

 scaly coverings, composed of organized layers of cells, are 

 more resistant than mucilaginous coverings, composed of 

 disorganized layers of cells. 



In both Wheat and Barley as a result of the action of 

 absolute alcohol cracks may be formed in the endosperm 

 of the seed. These are the result of the withdrawal of 

 water by the alcohol, but their formation, provided that 

 they do not pass through the embryo, does not necessarily 

 involve the destruction of vitality. 



It must be remembered that the effect of the absolute 

 alcohol upon the seeds is twofold. The first effect, and 

 this commences as soon as the seeds come into contact 

 with the alcohol, is to cause a gradual withdrawal from 

 the seed of the last traces of uncombined water which it 

 may contain. This operates injuriously upon the seeds 

 diminishing their vitality and may of itself alone cause 

 their death. The alcohol itself on the other hand only 

 comes into action when it has penetrated the seed coat. 

 This, the second effect, is to cause a rapid destruction of 

 the vitality of the seeds. 



In order to clearly distinguish between these two effects 

 and also in order to enable an estimate to be made of in 

 what degree the preservation of vitality, is due to the 

 protective seed coat and in what degree to the inherent 



