138 



PLANT ANATOMY. 



and on roots in the shape of small 

 rounded or oval or warty elevations of 

 looso and irregular c-orky tissues; this 

 looseness of arrangement of the cells 

 allows of the free exchange of gases to 

 the stem that otherwise could not occur. 

 Intercellular Spaces, These exist be- 

 tween the cells of plants partly in order 

 to allow the gasus taken in by the sto- 

 mata and lenticels to go to all parts of 

 the plant, and conversely to allow the 

 products of oxidation and other products 

 of gaseous interchanges to escape. Such 

 spaces are found in most tissues o.f the 

 plant, save the epidermis. Thoy vary 

 greatly iu shape and size, and are often 

 filUMl with products of secretion and ex- 

 cretion, to be later discussed. They fre- 

 quently serve as carriers of water and 

 are quite common in plants growing in 

 marsliy grounds. (Fig. 51.) 



FigT; 51.— Cross section of Bhizome Calamus 

 sliowin^, i, mtercellular spaces. *. starch con- 

 anotinff parenchyma. 0. oilceUs, G.ff. concentric 

 vessel bundle with xylem surrounding phloem. 

 (Tschirch. 



4. CONDUCTING SYSTEM. In the 

 lowest plants there is no conducting sys- 

 tem proper. The cells lying either sing- 

 ly, in chains or surfaces, absorb freely 

 the necessary food materials, each for it- 

 self. In the higher Thallophytes, the 

 seaweeds and mushrooms are met modi- 

 fications which foreshadow a conducting 

 system in plants; but only in the Bryo" 

 phytes, in the mosses proper, is there to* 

 be found a true series of elongated cells 

 set apart to do an especial work in the 

 conduction of food materials. From the 

 mosses on upward the conducting system 

 becomes more complete and more intri- 

 cate. At first it is a simple string of 

 elongated tubular cells. Later it devel- 





ops into a system which it is the purpose 

 here to describe. 



It can readily be seen that as plants 

 get larger the growing tips, as the leaves 

 and the flowers, are further removed 

 from the source of supplies, i. e., the 

 roots, and there must be established a 

 quick line of communication between the 

 extremities, hence the necessity for a 

 system of cells capable of transporting 

 and communicating fluids, both from the 

 root to the leaves and from the leaves 

 Lack again to the roots. 



The groups of tissues of the conduct- 

 ing system, together with the mechanical 

 fibres that support them, and w^hich 

 have been already described are called 

 the Fibro-Vascular Bundles. 



As the elements of the Fibro- Vascular 

 Bundle have all been developed from the 

 same primary meristematic tissue, it is 

 but reasonable to remember that all de- 

 grees of variation will be found in a 

 careful study of the elements of such a 

 bundle. For convenience, however, the 

 typical elements have been distinguished 

 from one another, and named. 



Naegli has divided the Fibro-Vascular 

 Bundle into two parts, from a purely 

 anatomical standpoint. One he calls the 

 Xylem. or the woody portion, and the 

 other the Phloem, or the bast portion. 



According to his classification the 

 Xylem contains 



Wood fibres, 



Vessels, 



Parenchyma, 



The Phloem contains 

 Bast fibres, 



Sieve tubes, 



Parenchyma. 



Haberlandt has proposed a classifica- 

 tion which divides the bundle into parts 

 more in accordance wnth the physiologi- 

 cal functions of the plant, as follow^s: 



1. Vessel portion— Hadrom. 



(a) Vessels, 



(b) Tracheids, 

 conducting water, 



(c) Woody parenchyma, conducting 

 water and plastic materials. 



2. Sieve portion— Leptom. 



(a) Sieve tubes and accompanying 

 cells, 



(b) Cambiform cells, 

 conducting plastic materials. 



(c) Accompanying cells (Geleitzel- 

 len). 



