Varietäten, Descendenz, Hybriden. — Physiologie. 601 



gers doux, 10 pour 100 etant des Bigaradiers et des Mandariniers. 

 Ces derniers n'ont pas fructifie encore d'oü leur determination pe- 

 nible. D'apres l'auteur, il en resulterait: 



1° que le Bigaradier, qui ne parait pas s'hybrider facilement 

 avec l'Oranger doux, s'hybride avec le Mandarinier; 2° que ces hy- 

 brides sont fertiles. 



L'Oranger doux {Citrus Aurantium) , qui est generalement con- 

 sidere comme une espece nee dans les cultures, peut etre obtenu 

 par l'effet du croisement d'un Citrus nobilis et d'un C. Bigaradia. La 

 couleur verte des embryons, si caracteristique du Citrus nobilis, se 

 maintient dans les embryons des hybrides ä fruits amers observes 

 jusqu'ä ce jour. L. Blaringhem. 



Blackmail, J. J., British Association for the advance- 

 ment of Science, Section K, Botany. Presidential Ad- 

 dress. (Report of the Assoc. Dublin 1908. p. 884-901. 5 fig. See 

 also: Nature XCVIII. p. 556-564. 1908.) 



The manifestations of the Principles of Chemical Mechanics in 

 the Living Plant. 



The address opens by directing attention to the fact that the 

 point of view from which the chemist regards the reaction taking 

 place in his test-tube has undergone a change in the last twenty 

 years, a change bringing it more into uniformity with that of the 

 biologist. No longer content with an equation as a final and füll 

 expression of a given reaction, the chemist now studies with minu- 

 test detail and with quantitative accuracy the progressive stages ot 

 development of the reaction and the effect upon it of varied external 

 conditions, of light, temperature, dilution, and the presence of 

 traces of foreign substances. 



This change has largely come about by the study of socalled 

 'slow' reactions and it is of these that the vital changes in living 

 animals and plants consist. The precise quantitative study of Che- 

 mical reactions has grown into the almost independent branch of 

 study known as physical or general chemistry which deals with the 

 fundamental universal laws of chemical change which hold through 

 all the families genera and species of chemical Compounds. If these 

 laws are fundamental with all kinds of chemical change they must 

 be at work in the living metabolic changes. If the chemical changes 

 associated with protoplasm have-any important factor or condition 

 quite different from the State of things which holds when mole- 

 cules react in aqueous Solution in a testtube, then it might happen 

 that the Operation of these principles of physical chemistry would 

 be obscured and not very significant, though it is inconceivable that 

 they should be really inoperative. 



The intention in this address, then, is to examine the general 

 phenomena of metabolism in an attempt to see whether the Opera- 

 tions of these quantitative principles are traceable, and if so how 

 far they are instrumental in giving a clearer insight into vital 

 complexity. 



Failure to recognise the action of the principles has been lar- 

 gely due to the dominance, in plant-physiolo^y, of the conception 

 of protoplasmic irritability. It is quite customary to consider that 

 every change in which protoplasm takes part is a case of the 

 'reaction' of an 'irritable' living substance to a 'Stimulus'. 

 Now this general conception of protoplasmic irritability, of Stimuli 



