AMOUNT OF WATER CIRCULATING IN PLANTS. 23 



why, in cryptogamous plants, none whatever is necessary; it should show, among the 

 varieties of animal races, why this or that mechanism is employed ; why insects have no 

 heart, or why in fishes the aorta resembles in mechanism the portal vein of the mam- 

 malia. In those more elevated tribes whose functions require that several circulations 

 should be simultaneously carried on, it should give a clear account of the mechanism 

 for them, whether they be systemic, pulmonary, or portal. The character of a true 

 theory is its extensive and clear application -to all individual cases. 



60. In this and the following chapter, I propose to explain what appear to be the 

 true mechanical principles of the general circulation of organized beings. For some 

 years past I have taught these doctrines to the medical classes of this University, though 

 until now they have not appeared in print. Founded as they are on principles strictly 

 physical, they form an important portion of the views set forth in this work. If among 

 plants light is the great agent of organization, electricity is the great motive force, which, 

 under a specific modification, determines the movements of nutritious juices. The im- 

 ponderable agents are the vital principle of organized systems. 



61. It will be perceived that the doctrines here given apply to all cases ; they are 

 also in harmony with physiological knowledge. They embrace not only the vegetable 

 and animal world, but the specific instances in each. In individual cases, they give an 

 account of the mechanism of the various circulations, whether they be systemic, pulmo- 

 nary, or portal. They also will be found to apply to those abnormal cases which arise 

 in disease, and offer an exact prediction of what should take place in inflammation and 

 asphyxia. 



62. First, therefore, let us take up the consideration of the circulation of the sap in 

 flowering plants, and show the physical conditions on which it depends. In the follow- 

 ing chapter we shall apply the same principles to the circulation of the blood. 



63. Early in the spring, in the'Southern States, the farmers plant their corn the 

 Zea mays. In the course of some days, if the weather is warm and favourable, the seed 

 begins to germinate, and presently the young plant appears above the soil. As soon as 

 this has taken place, the shoot turns green, the radicles begin to extend themselves, and 

 growth rapidly sets in. In a few weeks the plant has risen to an altitude of several 

 feet, and exposes its large green leaves to the sun. By the end of July, or the middle 

 of August, its maximum height is attained, and, under favourable circumstances of cul- 

 ture and season, so great is that height, that a man on horseback cannot touch the tas- 

 sel which adorns the top of the plant with a walking-stick. All this enormous evolu- 

 tion of organized structure has, in the course of a few days or weeks, originated from 

 a seed buried in the ground a seed which weighed but a few grains. 



64. From the roots to the top of the plant, large quantities of fluid are constantly 

 passing, and large quantities are thrown off from the leaves by evaporation. All this 

 water is obtained entirely from the soil, and all the carbonaceous matter which con- 

 stitutes the solid part is derived from the atmosphere ; and, inasmuch as even the water 

 itself descended originally from the air in showers of rain or drops of dew, we are justi- 

 fied in saying that this immense mass of organized matter is nothing more than a por- 

 tion of the atmosphere, which has been condensed and fashioned in a few weeks by the 

 agency of the imponderable principles. 



