556 OIIGANOLOGY. 



principally to the former, for through it all the currents must pass ; 

 whilst, on the other hand, the processes of secretion principally 

 take place through the leaf. 



220. No essentially different functions can be attributed to 

 the different forms which the axis exhibits. With regard to the 

 distinction of the two poles, the root and the axis, in a limited sense, 

 the former is frequently an organ of attachment, which fixes the 

 plant in a certain spot, and, from its being in contact with fluid 

 matters, serves especially for the absorption of nutriment ; it is 

 likewise a secreting organ, and, through the formation of buds, 

 serves the reproduction of the plant. 



That none of these functions are essentially and exclusively con- 

 nected with the roots, is proved by their never being found in 

 Mosses and Liverworts ; and also by their undeveloped state in so 

 many other plants, for instance, many Grasses, Nelumbium, c. ; 

 and finally, their decay in other plant?, for instance, in Ferns, 

 Palms, Cuscuta, &c. Their absence in all these plants is not 

 supplied by secondary roots, which might wholly or in part perform 

 these functions ; for instance, Ceratophyllum remains perfectly 

 rootless in every sense of the word. 



The functions of the axis, in a limited sense, can only be divided 

 according to anatomical systems, and not according to its various 

 morphological organs. The vascular bundles, where they exist, 

 serve in their youngest parts (the cambium) for the distribution of 

 the sap ; in their older parts they serve as a stiff and firm hold 

 (skeleton) for the plant. The parenchyma assimilates, and forms all 

 the peculiar substances which occur in the plant. Its external 

 parts (back and epidermis) serve for the absorption of nutritive 

 fluid, and also for secretion in plants under water, and for respira- 

 tion and transpiration in plants exposed to the air. In their sub- 

 sequent state, after the cellular layers of the bark have been 

 formed, the bark serves, on account of its being a bad conductor of 

 heat, as a means of maintaining the temperature of the interior of 

 the plant. Finally, the axis is an important organ of reproduction, 

 on account of its frequent regular and irregular development of 

 buds. In peculiar forms, as in cirrhi or in climbing plants, the axis 

 becomes an organ of attachment. 



221. The leaves are mostly very independent of each other, and 

 exhibit great variety in their chemical processes, according as they 

 are stem-leaves or flower-leaves. The stem-leaves, being those parts 

 of the plant which expose the largest surface to the air, form prin- 

 cipally the organs of respiration and transpiration, as also of various 

 secretions. In plants growing under water, they serve for the 

 absorption of fluid nutritive matter. By the formation of buds they 

 become organs of reproduction. The leaves in the region of the 

 organs of fructification frequently exhibit a very weak vegetation, 

 and easily die altogether (for instance, the pappus, the bracts, and 



