lOO 



NA TURE 



[November 25, 1909 



or seed? Does the cessation of the vital activity 

 afford it any increased power of growth or vigour 

 of constitution ? Is it only a condition induced by 

 circumstances, or does it speak of a rhythmic tendency 

 inherent in the plant? 



More interesting still — Is the resumption of life 

 which we call germination an evidence of the attain- 

 ment of such increased vigour, or is it merely the 

 resumption of ordinary chemical change when inhibit- 

 ing conditions are removed ? In the latter case, is 

 the living substance concerned in setting up such 

 chemical changes, or do these arise without such 

 initiation ? 



If we study the germinative changes we find them 

 associated universally with the existence and activity 

 of enzymes. The resting germ, whether the structure 

 be seed or spore, is surrounded by food material 

 deposited for its ultimate nutrition, but needing 

 enzymic action to render it suitable for actual 

 assimilation. The number of such enzymes known to 

 physiologists has increased most remarkably during 

 the last decade, and though they have been found to be 

 most plentiful in seeds, the study of the spore has 

 shown that it is similarly equipped, though from its 

 unicellular character the distribution of the enzymes 

 is much simpler. At a certain moment the germ 

 starts into life, simultaneously the enzymes are found 

 at work, and nutritive pabulum is presented to it in 

 assimilable form. Which is cause and which effect? 

 Does the living substance, awaking from a sleep, 

 start the enzymic activity, or do the enzymes originate 

 the change? Is the activity of the living substance 

 itself due to enzyme action? In other words, is life 

 a question of the existence and activity of enzymes? 



These subjects can be studied more advantageously 

 in a seed than in a spore on account of the physio- 

 logical as well as anatomical differentiation which it 

 presents. It is easy to distinguish the germ which, 

 after resumption of growth, becomes the new plant, 

 and to separate it from the stores of food which are 

 laid up for its nutrition, and which will be the sphere 

 of activity of the digestive enzymes. These stores 

 may be within it or lying around it, but they in any 

 case are well away from its actual growing points. 

 In such a seed, then, we can distinguish the germ, or 

 embryo, the new plant, and the remains of the parent 

 which has given it origin, this being sometimes large, 

 sometimes small, in proportion to the former. 



.'Vt the outset we may ask, what is the actual con- 

 dition of these two parts? How far can we find 

 evidence of life in either during the period that elapses 

 between the severance from the parent plant and the 

 resumption of growth and activity after the resting 

 stage? If we study the phenomena of life in the seed 

 as a whole, we are led to apply to it the 

 test of the existence and maintenance of respira- 

 tion, this being the inseparable accompaniment 

 of metabolic change and hence a constant 

 feature of life in the various conditions with 

 which we are acquainted. If we rely on either the 

 absorption of oxygen or the exhalation of carbon 

 dioxide, however, we shall be obliged to deny the 

 presence of life in the seed at all. Many and careful 

 examinations have been made of the respiratory pro- 

 cesses in seeds of many descriptions. Perhaps the 

 most exhaustive of them were those of Romanes in 

 1803. Seeds of various plants were kept in glass 

 tubes which had been exhausted so completely that 

 thev contained only one-millionth of an atmosphere, 

 and were left for upwards of a year. This treatment 

 did not hinder their subsequent germination. Some 

 of them were afterwards immersed in various inert 

 gases, such as hydrogen and nitrogen, others placed 

 in carbon monoxide, sulphuretted hydrogen, vapours 

 NO. 2091, VOL. 82] 



of ether and chloroform, and kept thus for twelve 

 months, still without any deleterious effects. It seems 

 hard to suppose them living in the usual acceptation 

 of the term. In 1892 Jodin imprisoned some seeds in 

 ordinary air in hermetically sealed flasks ; he kept 

 them so for four years, and examination of the air at 

 the conclusion of this term showed its composition 

 absolutely unchanged, no exhalation of carbon dioxide 

 having taken place. Respiration, as ordinarily under- 

 stood, thus seems to be quite in abeyance. 



The suspension, if not disappearance, of life during 

 this resting period is emphasised by the behaviour of 

 the seeds under exposure to extremes of temperature. 

 Observations made by Wartmann so long ago as 

 i860 showed that germination was not prevented by 

 preliminary exposure of the seeds to temperatures 

 ranging from —40° to —78° C. This does not seem, 

 however, to prove the point, for the normal tempera- 

 ture of agricultural land in Siberia in winter is almost 

 as low, often reaching —60° C. Experiments were 

 made by de Candolle and Pictet in 1879 which carried 

 the range of temperature a little further, but the 

 most drastic treatment was rendered possible by the 

 liquefaction of air. Elxperiments with the aid of this 

 powerful reagent have been made in France by Pictet, 

 and in England by Brown and Escombe and by Sir 

 W. Thiselton-Dyer, with the result that such extreme 

 cold had very little effect in inhibiting the power of 

 subsequent germination. 



At the other end of the thermometric scale strange 

 results have been found, many seeds having been 

 proved capable of germinating after being exposed 

 for a short time to temperatures higher than the 

 boiling point of water. So long ago as 1877, Just 

 heated seeds of a species of Trifolium to 120° C. with- 

 out injuring their power of development. Some years 

 later a more extended series of experiments was 

 carried out by Dixon on seeds selected from several 

 natural orders, all of which withstood, without injury, 

 a temperature of about 105° C. prolonged for several 

 hours. Their vitality and power of development were, 

 however, much mere easily affected by heat than by 

 cold. 



This resistance to great extremes of temperature 

 has been found to be correlated in a considerable 

 degree with the state of desiccation whicli was char- 

 acteristic of the seeds. Hence is lent some support 

 to the view of the dependence of germination on 

 enzymic action, for the latter can only be exercised 

 in the presence of water. Some experiments carried 

 out by Acton in 1893 seem to show that even the 

 small amount of water in the wheat grain enables a 

 certain amount of digestive change to take place in 

 both the proteins and the carbohydrates of the grain. 

 In the absence of all moisture the enzymes remain 

 quiescent. 



As it is generally accepted that chemical action 

 cannot take place at temperatures so low as those 

 specified, and as .chemical change or metabolic 

 activity is an inevitable accompaniment of life as 

 defined by Herbert Spencer, the idea that germina- 

 tion is dependent upon the continued and permanent 

 life of the protoplasm in the resting seed, there have 

 been many efforts made to explain these anomalous 

 manifestations. C. do Candolle concluded that after 

 a certain time the protoplasm of the ripe seed passes 

 into a state of complete inertness, in which it is 

 incapable of either respiration or assimilation, and 

 that while in this condition it can support, without 

 detriment to its subsequent revival, rapid and con- 

 siderable lowering of temperature. Indeed, the access 

 of cold to a seed seems to be only injurious as it can 

 bring about the freezing of the water remaining in 

 it, with the subsequent thawing as the temperature 



