360 PHYSIOLOGY OF NUTRITION. 



The latex reservoirs of plants are of very different kinds. A 

 very favourable object for study is found in the root of Scorzonera 

 hispanica (black root). We employ alcohol material, and after 

 removing the superficial layers of cortex prepare tangential 

 longitudinal sections. The latex reservoirs, readily recognised 

 by their contents, appear in our preparations as elongated vessels, 

 frequently anastomosing with one another, and traversing the 

 small-celled parenchyma. 



We further submit to examination stems of Chelidonium majus, 

 using alcohol material. Transverse sections show the epidermis, 

 collenchyma, and green cortical parenchyma. These are followed 

 internally by a closed ring of mechanical tissue, whose elements 

 are strongly thickened. The vascular bundles consist of a bast 

 portion and a wood portion. In the bast, but also in the ground 

 tissue surrounding the fibre-vascular bundles, we perceive ele- 

 ments with brown contents. These are the latex vessels. The 

 latex of Chelidonium has an orange-red colour in the fresh 

 state. The treatment of the material with alcohol has caused 

 the latex to coagulate in the laticiferous vessels. 



145. Accumulation of Material. 



It is clearly an important fact that some tissue-complexes in 

 the plant serve as channels of conduction, others as places for 

 the deposition of particular substances. We are not at present 

 in a position to give a detailed account of the causes of the 

 phenomena. It is only possible to do so in a general way, and 

 I have already discussed these matters in my Lehrbuch der Pflan- 

 zenp hysio logic . 



If, e.g., an accumulation of starch is to take place in the tissues 

 of the reserve receptacles, causes must be at work in their cells, 

 which bring about the precipitation, in the form of starch grains, 

 of the non-nitrogenous material conveyed thither. Similar causes 

 must also be operating in the transitory formation of starch 

 in the cells of the tissues which act as channels for the con- 

 duction of carbohydrates. The accumulation of starch can only 

 take place in cells in which starch-formers occur, and their 

 activity is the necessary condition for a continuance of the 

 current of dissolved carbohydrate. The results of the following 

 experiments serve to afford us an idea of the nature of the 

 process of accumulation. 



