CHAPTER I. 

 INTRODUCTION: THE LIVING PLANT. 



THE study of plant life which in its fundamentals is physico- 

 chemical, is in its broad aspect the study of the origin of 

 life, since the plant arrived before the animal had its being. 

 This attitude is frankly mechanistic, to some minds grossly 

 materialistic, but more progress may be anticipated by follow- 

 ing mechanistic hypotheses than by the pursuit of theses based 

 on foundations the stability of which is not yet agreed on. 

 The present state of knowledge, however, does not permit 

 a full physico-chemical explanation even of phenomena ap- 

 parently purely chemical, and sooner or later a stage is 

 reached when agencies of a vitalistic nature have to be 

 offered in explanation. 



The problems immediately involved may best be ordered 

 and formulated by a consideration, intentionally elementary, 

 of the history of a seed planted in good ground. The period 

 of rest completed, a period which varies much in duration 

 and in different species,* a sowed seed begins its germination 

 by the imbibition of water, provided the conditions, chiefly 

 of moisture, temperature and aeration, are suitable. When 

 the seed coat is saturated, water is absorbed by the under- 

 lying structures both by imbibition and by osmosis, for the 

 seed coat, although it may be impermeable to certain sub- 

 stances,! is permeable to water. Considerable swelling com- 

 monly results so that the volume of the seed is much increased 



* The period of dormancy and consequently the beginning of germination 

 are conditioned by such factors as the degree of permeability of the seed coat 

 to water, the mechanical restraint imposed upon the embryo and associated 

 structures by the rigidity of the testa, the necessity of an after-ripening process 

 for the embryo, the degree of humidity, the amount of carbon dioxide, the 

 presence or absence of light, and the degree of temperature. See Crocker : 

 "Amer. Journ. Bot.," 1916, 3, 99; Kiihn : " Ber. deut. bot. Gesells.," 1916, 

 34, 369 ; and Crocker and Harrison : " Journ. Agric. Res.," 1918, 15, 137. 



tSee Adrian Brown: "Ann. Bot.," 1907, 21, 790; " Proc. Roy. Soc.," 

 Lend., B. 1909, 8z, 82. 

 VOL. II. I 



