THE FL0WE1UNG PLANT. 



and root-hairs, by means of osmosis, much as described on p. o„ 

 The particles of soil are also more or less corroded by the acid sap 

 of the root-hairs, &c, to which they closely adhere (fig. 3). This 

 permeates the cell-walls with which the particles 

 come into close connection. If the roots of a 

 plant are allowed to grow over a polished slab 

 of marble, this will be corroded at the points of 

 contact, and a kind of rough etching of the 

 root system produced. Roots thus help in the 

 preparation of the solutions which they absorb. 

 This solvent action is aided by the carbon 

 dioxide excreted in respiration. The roots of 

 water plants can easily avail themselves of the 

 surrounding medium with the substances dis- 

 solved in it. Parasitic roots come into such 

 close relation with the tissues of the plant preyed 

 upon, that they form a physiological part of it, 

 and can by its means receive not only simple 

 food, but also material that can at once be built 

 up into protoplasm. 



Circulation of Liquids. — The substances ab- 

 sorbed by the root ultimately reach the leaves 

 by various routes and in various ways. Just as 

 they can enter the root-hairs and young epider- 

 mal cells by means of osmosis, so can they in 

 the same way reach cells that are more deeply 

 situated, and so on. We also know that liquids 

 travel very largely by means of certain vessels 

 (cf. p. 41), chiefly, as one would expect, in their 

 interior. This has been noticed for a very long 

 time in the - case of vines. When these are 

 pruned in spring, a great deal of sap exudes 

 from the cut surfaces. In popular language, 

 the plant " bleeds," and careful examination 

 shows that the liquid oozes out from the 

 cavities of the vessels. This phenomenon was 

 formerly ascribed to a mysterious force called 

 pressure, operating before the leaves unfold. It was 

 erroneously supposed that at other times liquids travel only in 

 the walls of the vessels, and not within them. 



Roots may perform another important office in nutrition, i.e., 

 the storage of reserve materials, which are supplies of nutriment 

 destined for use at some future time. The matter is chiefly stored 

 as starch, but it may assume other forms, e.g., cane-sugar, as in 

 the beet -root. 



Fig. 3.— Seedling of 

 White Mustard [from 

 Sachs]. A. as taken 

 out of the soil with 

 particles of earth 

 clinging to the root- 

 hairs; in B these 

 have heen removed 

 by washing in water. 

 Above are seen the 

 two green expanded 

 cotyledons; between 

 these and the root- 

 hairs, the hypocotyl. 



root 



