in PHYSIOLOGICAL VARIATION IN SEEDS 139 



sensitiveness of different species in regard to the same 

 reagent ; 2ndly, marked differences occur also in 

 regard to the sensitiveness of different individuals oi 

 the same species in regard to the same reagent. 



I am at present engaged in repeating and develop- 

 ing this series of experiments, as they help to illus- 

 trate physiological variability, and can be used also for 

 investigations in selection. Of course, in many cases 

 the result may be interpreted as due to variation in 

 the thickness of the seed-envelopes, or in the bulk 

 of the seed itself; but whatever the cause of the 

 differences in resistance may be, the main point is 

 to demonstrate palpable variations, that is, a firm 

 basis for the operation of selection ; and, on the other 

 hand, the differences in thickness of the seed-en- 

 velopes is not a mere anatomical fact, it is also a 

 physiological character of the plant. 



Observation has, however, already provided very 

 interesting facts bearing upon this question of physio- 

 logical variability in regard to the influence of poison. 

 We know that this influence varies according to many 

 conditions, among which are the following : 



First, the mode of introduction, Many poisons are 

 devoid of danger when introduced through the ali- 

 mentary tract, while they are very dangerous when 

 introduced into the blood or under the skin, because 

 in the first case they are slowly absorbed or are 



