Miscellaneous. 



358 



[OCTOBER, 1909. 



pure cellulose walls ate impervious to 

 air when completely dried. 



These dry integuments are also quite 

 impervious to other gases, and to ether, 

 chloroform and alcohol ; the germ in the 

 seeds is thus hermetically sealed beyond 

 the reach of poisons, and this explains 

 why seeds are not killed when kept for 

 months in ammonia, sulphuretted hydro- 

 gen, alcoholic corrosive sublimate and 

 other noxious substances. Such results 

 in the past have been held to prove 

 that the dormant protoplasm of the 

 seed was in some special resistant, in- 

 sensitive condition. Now we know that 

 the protoplasm of the germ is not 

 reached unless the testa be perforated ; 

 if this be done, then the seeds never 

 survive contact with such poisons. 



A philosophical question of great signi- 

 ficance for our conception of the nature 

 of life underlies these enquiries into the 

 longevity and vitality of seeds, namely, 

 the question whether it is possible for 

 vital changes to be absolutely arrested 

 without death — irrevocable death— re- 

 sulting. 



Some observers have held that the 

 resting seed is in a condition of retard- 

 ed vital activity ; others, that all vital 

 activity is completely arrested. It is 

 clear, even on the former view, that 

 any vital changes in the seed ate very 

 slight and slow, so that experimen- 

 tally it becomes very difficult to de- 

 cide between these views : between no 

 change and a just perceptible change. 

 If it could be established that the living 

 seed passes, on drying, into a state of 

 complete rest, a state of " static equili- 

 brium " as opposed to the dynamic equili- 

 burium of the ever-changing living cell, 

 then this important, fundamental ques- 

 tion would be finally answered. 



The resistance of resting seeds to ex- 

 treme cold and to extreme desiccation 

 supports the view that the protoplasm is 

 here in a state of static equilibrium quite 

 analogous with the condition of a charge 

 of explosive before it is started into 

 action by spark or blow. 



Prof. Becquerel's work shows that it 

 is impossible for a seed perfectly devoid 

 of moisture to conduct the gaseous ex- 

 change involved in the process of res- 

 piration. Some observers have stated 

 that resting dry seeds continuously 

 produce carbon dioxide, while others 

 have failed to confirm this. It now 

 turns out to be chiefly a question of 

 whether the seed contains enough of 

 water for its integuments to be per- 

 meable to gases. In this connection it 

 must be remembered that so-called dry 

 seeds of commerce contain 5 to 15 per 

 cent, of water, and that it takes months 

 to dry off all this water from them 



It seems quite clear that if the seed is 

 completely dried no detectable amount 

 of respiration takes place within long 

 periods of time. 



As regards cold, all observers are 

 agreed that the vitality of ordinary dry 

 seeds is quite unaffected by exposure 

 to the extreme cold of liquid hydrogen — 

 250°C. It is generally held that all 

 chemical chauge is in abeyance at such 

 a temperature, and that, therefore, the 

 seed cannot be in any other than a state 

 of static equilibrium. This would seem 

 to be true of such chemical changes as 

 are essential parts of vitality, though, 

 of course, a few violent chemical re- 

 actions do occur at this low temper- 

 ature. 



According to the modern conception 

 of the relation between temperature 

 and chemical change, with falling tem- 

 perature every reaction will go slower 

 and slower, but however low the tem- 

 perature change will be only retarded, 

 not absolutely stopped. The resistance 

 to cold cannot, therefore, finally settle 

 this question. 



We are, indeed, forced to conclude that 

 the resistance of dry seeds to temper- 

 atures as high as lOO'C. or even 120°C. 

 favours the view of static equilibrium. 

 If the protoplasm of resting seeds is en- 

 tirely at rest in static equilibrium, then 

 the viability of the seeds should endure 

 indefinitely, like the explosibility of a 

 properly stored charge of powder. It is, 

 however, notorious that in a sample of 

 stored seeds the percentage of germina- 

 tion steadily decreases. To what can 

 we attribute this loss of viability ? It is 

 suggested that just as the proper work- 

 ing of a charge of powder may be des- 

 troyed by accidents of storage such as 

 dampness, so in the case of stored seeds 

 the falling off is due to changes wrought 

 in them by oxidation or hydration. 



Seeds are very hygroscopic and absorb 

 water in direct proportion to the humi- 

 dity of the air. Jodin has recorded the 

 varying weight of seeds in different 

 meteorological conditions, and one of 

 the few, changing factors in an ordinary 

 resting seed stored in air must be this 

 alternate taking up and giving off of 

 water. Possibly the ceaseless, slight 

 molecular changes involved in this pro- 

 cess slowly disorganise the viable proto- 

 plasm and in time cause the death of the 

 seed. Prom such changes a hard " seed 

 would be exempt. It is therefore pro- 

 bable that complete desiccation and 

 preservation in a dry environment are 

 necessary conditions for testing the 

 maximum longevity for any plant whose 

 seeds are among the majority in which 

 the testa is not impermeable to water. 



