VITALITY AND GERMINATION OF SEEDS. 213 



observed. Peas which had been immersed in the solution 

 of HgCl 2 for one day shewed after treatment with Am 2 S a 

 black rim nearly a millimetre deep all over the cotyledons, 

 the plumule was untouched, the inner surface of the 

 radicle very slightly blackened, but on the outer surface 

 and tip the HgCl 2 had penetrated for one third the thick- 

 ness of the radicle, i.e., right into the growing point in 

 most cases. In a few of the Peas the blackening was 

 restricted to a mere film on the outer side of both radicle 

 and cotyledons and these Peas were still capable of 

 germination. After two days immersion the Plumule, 

 the Hypocotyledonary axis, and the central part of the 

 base of the radicle were still untouched but the tip of the 

 radicle was quite permeated. 



In the case of the Haricots the HgCl 2 penetrates the 

 entire radicle and tinges the surface of the plumule in a 

 single day. In two days the entire embryo is permeated 

 by the salt. 



Both Peas and Haricots absorb water with about equal 

 rapidity, the majority being soaked through in from 5 to 

 6 hours at ordinary temperatures. It therefore follows 

 that the water penetrates the seeds with at least ten times 

 the rapidity that the salt does and also that the integuments 

 and substance of the Haricots are more readily permeable 

 by HgCl 2 than those of Peas. 



One reason why the mercuric chloride penetrates the 

 seeds so much more slowly than the water in which it is 

 dissolved is probably because as it enters the seed it com- 

 bines with the proteid constituents of the seed. That 

 such a combination occurs is shewn by the change which 

 occurs as the mercury salt penetrates the substance of the 

 seed, the latter becoming whiter and more opaque, and 

 also by the extreme difficulty of washing out the salt 

 from the tissue of a seed which it has thoroughly perme- 



