TISSUES AND SIMPLE ORGANS. 99 



tlie innermost (primitive) vessels incline most strongly toward the 

 outside, the next following less strongly, etc. The accompanying 

 figure (59) represents the latter displacememt for the left side. 



A certain regularity also exists in the union of the bundle-ele- 

 ments of root-branches with the corresponding elements of the 

 main root. Without entering into the particulars of these and 

 similar structural relations, we will direct attention to the fact that, 

 in the majority of cases, the outer angle of a vascular plate of 

 the main root is that to which the secondary vascular system 

 becomes united. The vessels of both roots unite ; the leptome- 

 groups are derived from the immediate vicii'ity. 



(i) The Special Physiology of the Movements of Food-substances 

 and Water in Plants. 



The paths in which, and the forces through which, water and 

 food-substances are moved will next claim our attention. 



Movement of the above-mentioned substances must take place. 

 Carbohydrates, especially starch, must be transported from the 

 places of formation to the centres of nutrition, and eventually to 

 the storing tissues ; and again from the latter to the centres of 

 nutrition : or, in other words, from the green assimilating organs 

 to the tubes and stems, to developing roots, flowers, seeds, etc., 

 and from tubes and other storage- tissues to the places of organ- 

 formations, such as the root-tip, the apical area of the stem, etc. 

 Farther, the organs of great surf ace -exj^ansion (leaves) require a 

 large quantity of water, for purely physical reasons (on account of 

 evaporation), which must be conducted upward from the roots. 



a. Conduction of Albumen. 



Investigations concerning the seat of alhumen-ioTrcisiion (Frank, 

 Schimper) have perhaps already proceeded so far as to show that 

 every living cell (not only the green ones) which contains nitrates 

 and a corresponding C-bearing substance may be considered as a 

 centre of amide-formation, and secondarily also of albumen. 

 (Plasm is an essentially albuminous substance.) We, however, 

 at once meet with difficulties in trying to explain the circulation of 

 albuminous substances. Some uncertainty has recently arisen as 

 to whether the sieve-tube tissue should be considered as albumen- 



