JDI.T 1, 1892.] 



KNOWLEDGE 



136 



emphasize here is, that the protoplasm is the vital portion 

 of the plant, and that from it all the parts of the plant are 

 formed. Hence, in order to keep a plant alive, we must 

 supply it with material containing the elements which enter 

 into the constitution of protoplasm. Sachs speaks of ''the 

 universally known and yet essentially unknown protoplasm" ; 

 it is essentialh/ unknown, although, as the result of various 

 chemical researches, its chemical composition has been 

 roughly determined. Its chemical formula cannot be 

 given, nor is this to be wondered at in the case of a body 

 which is living, and hence probably constantly undergoing 

 change. It is made up of proteids. complex compounds 

 of oxygen, hj-drogen, nitrogen, and sulphur, and when it 

 is alive water is always present in it. If it be burned, 

 these materials go off in the form of gas, but there remains 

 behind an incombustible portion or ash. in which are 

 present potassium, magnesium, calcium, phosphorus, and 

 sulphur, in addition to other substances. All these ele- 

 ments — carbon, hydrogen, oxygen, nitrogen, sulphiu*. 

 phosphorus, potassium, magnesium, and calcium — must 

 be supplied in some form to a plant in order that it may 

 live ; for of these is its vital substance, or protoplasm. 

 buUt up. 



It remains for us now to detennine in what manner 

 these materials are taken in by a green plant, and what is 

 their fate after absorption. The higher plants are those 

 which are brought more immediately under our notice in 

 our daily walks. We will, therefore, consider their method 

 of feeding, premising, however, that it does not differ 

 essentially from that of any green plant, however humble : 

 but it will be useless to attempt a description of this until 

 our readers have a clear notion of the structure of one of 

 these. The remaining portion of this paper is thus 

 devoted to an account of the anatomy of the elm tree — a 

 typical dicotyledon. 



It has a much branched root that it sends into the soil, 

 and a stem branching in the air and bearing the leaves. 

 The ultimate ramifications of the root are fine fibrils. 

 These are its important portions. The tip of each rootlet 

 is clothed with a cap (Fig. 2, r.c), to prevent the growing 

 tissue (t) situated immediately behind it 

 from being damaged as the root pushes 

 itself through the soil. As constantly 

 as the outer layers of tissue are rubbed 

 away, new ones, formed by the growing 

 tissue, take their place. The root cap is 

 thus being constantly renewed. At a 

 slight distance behind the cap unicellular 

 haks are apparent. In a cross section of 

 the root taken at this point it becomes 

 evident that these are prolongations of 

 some of the epidermal or outer skin cells 

 (Fig. 3). The same figm-e shows the cortex 

 or rind to be made up of iso-diametric 

 cells containing protoplasm. The tissue 

 they form is called parenchyma tirx^a, 

 and 'iv^uaa, a tubei. Immediately beneath the cortex is 

 the endodermis or bundle-sheath I s^-Jo, within, and ospfxa, 

 the skin) enclosing a zone of tissue composed of delicate 

 cells, and called the pericycle. This in turn surroimds a 

 mass of tissues forming the vascular bundle. The vascular 

 bundle is a complex structure. It is composed of three chief 

 portions— the sylem, phloem, and cambium. The xylem 

 (0uXoy, wood) or wood is made up of parenchyma, of 

 elongated cells with walls spirally thickened and pitted 

 (tracheides), and of vessels. 



Vessels are formed by the fusion of cells placed end 

 to end, whose adjacent walls have broken down. The 

 tracheides and vessels contain no protoplasm. The cam- 



FiG.?. — Diagram- 

 matic longitudinal 

 section of apex and 

 front, r.c, root cap ; 

 t, growing tissue : 

 r.i,rascularbundle: 

 r.h., root hairs. 



bium is composed of thin-waUed cells densely filled with 

 protoplasm. Parenchyma and sieve-tubes are the con- 



-r*oo t ka.( r* 



Fig. 3. — Tmn-verse Section (semi-diagrammatic) of root. 



stituents of the phloem. The sieve-tubes have received 

 their name from the fact that their adjacent walls are 

 provided with apertures giving them the appearance of a 

 sieve, and sieve-plates are also at times present on their 

 lateral walls. The xylem and phloem alternate in posi- 

 tion with each other, and the cambium is placed between, 

 lying outside the xylem and inside the phloem. The 

 central portion of the root is occupied by the pith, which 

 is formed of parenchyma. From the medulla or pith pro- 

 ceed ravs of tissue — the meduUarv ravs. 





50 





^^^^ 



scL 



■c 



lo;"' 

 aooo:- 

 JOOQU 



Fig. i. — TransTerse Section of voung stem of Elm. epi, epidermis ; 

 c c, cork cambium ; ^Af .. phelloderm ; scl., sclerenchyma ; j>A., phloem ; 

 <:. cambium ; med. rays, meduIlarT ravs ; r. A., Taseular bundles. The 

 cork cambium forms cork towards the outside, and phelloderm 

 towards the inside. The phelloderm at this stage contains chloro- 

 phyll. The large openings in the ivlem are wood-Tessels. 



