140 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



less rapidly. This discovery gave rise to much experimental 

 work which is now too well known to be described here. 

 The suggestion was made by Armstrong (1909) that the 

 peculiar grouping of substances brought out by this research 

 might be due to the relation of the various compounds 

 to water, those which formed hydrates being held back, 

 whereas the remainder, which were not hydrated or only 

 feebly hydrated, possessed the power of penetrating the 

 seed coats. It is certainly remarkable that whereas 

 aqueous alcohol can pass into the seeds very freely, yet 

 when in the anhydrous condition this substance is unable 

 to enter. 



It was shown by Schroder (1911) that wheat possessed 

 the same type of selectively permeable coat. 



Quite recently Shull (1913) has added considerably to 

 our knowledge of the subject by his experiments on Xan- 

 thium glabratum. Seeds of this plant, carefully dried at 

 40 over phosphoric anhydride, were found to germinate 

 vigorously after prolonged immersion in ether, chloroform, 

 acetone, and absolute alcohol. It was not necessary to 

 remove the last traces of water from these liquids, this 

 point being tested directly. Moreover, even 95 per cent, 

 commercial alcohol did not kill air- dried seeds till after 

 over four days' immersion. This confirmed the previous 

 work of Giglioli (1882 and 1895), Dixon (1902) and Bec- 

 querel (1907), who, with the exception of the last-named, 

 had even treated seeds with saturated solutions of mercuric 

 chloride in methylated spirit. The dried coats of Xan- 

 thium seeds were also proved to be impermeable to oxygen. 



When placed in water, air -dried seeds of Xanthium 

 quickly absorbed over 50 per cent, of their original weight, 

 the process being rapid at first, and almost complete in 

 fifteen hours. In strong salt solutions the forces of capil- 

 larity and imbibition, as well as the attraction of colloids 



