134 



KNOWLEDGE 



[July 1, 1892. 



Sun is before the clock, one reads-from the preceding edge 

 of the shadow of the chib shaped bob on the gnomon, at the 

 place where its shadow cuts the hour line. 



One of Major- General Ohver's dials ruay be seen at 

 Messrs. Negretti and Zambra's shop on the Holborn 

 Viaduct. A. C Raxyard. 



THE FEEDING OF A PLANT. 



By -T. Pentland Smith, M.A., B.Sc, Lrcturn- mi Hotanii 

 lit the Hortiiiilfuinl Ciillrf/i', Sii'niili'i/. 



PLANTS take in their food material fi'om two 

 sources — the soil and the air. The manner of 

 its absorption depends upon the constitution of 

 the plant under consideration. So far as regards 

 the nourishing process, the vegetable kingdom 

 may be divided into two large classes — the first including 

 all those plants which possess green colouring matter, the 

 second those in which this green substance is conspicuous 

 by its absence. Our present consideration will be the 

 feeding of green plants, and we will preface our remarks 

 thereon by referring generally to the structure of these, 

 and specially to that of the higher members of the 

 series. 



The green plant detachment numbers in its ranks the ! 

 most simple structures and the most complex organisms. 

 The simplest are composed of a single sac or bag, which 

 we call a cell, and the highest members of the series are 

 built up of an aggregation of cells. " The true meaning 

 of the word ' cell ' may be quite clear to but few, the less 

 so since biologists themselves, even now, hold and discuss 

 the most different opinions upon it. To many, the cell is 

 always an independent living being, which sometimes exists 

 for itself alone, and sometimes 'becomes joined with ' other 

 millions of its like, in order to form a cell-colony, or, as 

 HsEckel has named it for the plant particularly, a cell- 

 republic. To others, again, cell-formation is a phenomenon 

 very general, it is true, in organic life, liut still only of 

 secondary significance ; at all events, it is merely one of ; 

 the numerous expressions of the formative forces which 

 reside in all matter, in ihe highest degree, however, in 

 organic matter."* 



Much has been written on the subject of the plant 

 structure, and the subject itself is an exceedingly interest- 

 ing one to the anatomist ; but to the general reader, at 

 least, anatomy, apart from physiology, is a dry study. 

 The two departments ought always to go hand in 

 hand. 



In the lowest plants, and in the lowest animals, a single 

 cell performs all the life-fimctions. As we proceed higher 

 in the scale of organization we notice that differentiation 

 takes place, and continues until, in the highest forms, a 

 complex series of tissues exists, each fitted for the per- 

 foi'mance of a definite work. In both kingdoms a mass of ' 

 protoplasm (irpwTO';, first, and ■jt'axitii.oi., form) constitutes the 

 simplest cell. The composition and fimction of proto- 

 plasm we will discuss presently ; it suffices in the meantime 

 to note that the lowest cell does not have a ceU-wall 

 distinct from the protoplasm. The cell composed of 

 protoplasm boimded by a wall may be considered as 

 occupying a step higher in the scale of organization. The [ 

 generality of unicellular, or one-celled plants, however, ' 

 are composed of such structures. 



The size ot the cell varies considerably. A bacterium 

 cell may be so small as to require the highest powers of 

 the microscope and the most accurate definition to 

 determine its form ; while it is still a matter of doubt if 



* Sachs' Physiologn of Plants, page 73. 



the branching tubes, filled with milky material, found in 

 species of Euphorbia are not composed of a single cell. 

 The hairs of many plants afford good instances of cells of 

 large dimensions. Let anyone who cuts up an orange 

 note the structure of the pulpy portion. A cursory exami- 

 nation will show him that it is built up of very large 

 elongated cells, filled with a juicy material. These cells 

 are the hairs of the inner wall of the fruit. And in no 

 less a degree does the shape of the cell vary, as we shall 

 see in our study of the tissues. 



The truly ^ntal portion of the plant and of the animal is 

 the protoplasm. By its activity are all the parts of the 

 body formed. The most complex plant and the most 

 highly organized animal have had their origin in a small 

 speck of protoplasm, and only so long as the protoplasm is 

 alive can these be said to be living beings. The low 

 power of a microscope reveals to us, in a drop of water 

 taken from the bottom of a muddy pool, a small unicellular 

 organism capable of locomotion and of alterating its form. 

 It is known as an Amcfba. Fig. 1 shows one of these 

 animalsin its various phases. 

 The processes marked ps 

 can be sent out or retracted 

 at will, and are called pseu- 

 dopodia (vJ/euJo;, false, and 

 Ttovi, a foot), or false feet. 

 By the protrusion and re- 

 traction of these processes 

 of its body the animal moves 

 from place to place, and 

 movement of this kind is 

 very common in the two 

 organic kingdoms, and is 

 termed amoebiform move- 

 ment. More careful exami- 

 nation reveals the lact that 

 the outer portion of the 

 body is clear and the inner 

 granular. The granular 

 parts are probably portions 

 of matter about to be formed into protoplasm, or which 

 have resulted from its decomposition. The mode of 

 taking in food is also observed to be a very simple one. 

 The animal encloses it by its false feet and absorbs it mto 

 itself; and its method of ridding itself of what it does not 

 require, or cannot make use of for its nourishment, is no 

 less complex — it ejects it at any spot on its surface. 

 When it has grown large enough it breaks up into two 

 pieces, and each portion so formed is a new Amceba, 

 capable of performing the work which its parent pre- 

 viously did. All this can be seen very easily under the 

 microscope. Amoebfe are not difficult to procure. For 

 these reasons we have selected this animal to illustrate 

 the work which a simple mass of protoplasm can perform. 

 We see then that the phenomena of locomotion, nutrition 

 (including ingestion, digestion of food, and ejection of 

 waste products), and reproduction are all exhibited by this 

 unicellular organism. To these we must add respiration, 

 or breathing, the taking in of oxygen and giving out of 

 carbon dioxide, which we know is also constantly going 

 on during the lifetime of plants and animals. 



In the higher plants the protoplasm is divided into 

 pieces by walls, so that the whole organism consists of a 

 number of chambers or cells. Each chamber in its young 

 condition is filled with protoplasm ; as they grow older 

 the protoplasm in many cases disappears and leaves only 

 the case in which it was contained, the cell-wall. The 

 wall has not an origin apart from the protoplasm, but is 

 deposited by the protoplasm itself. What we would 



ntJL. 



Fl&. 1. — Diagrammatic representa- 

 tions of various phases assumed 

 by an Amceba. The inner line 

 indicates the boundary between 

 the gi-anular portion or endosarc, 

 and the clear outer portion or 

 ectosarc; pi, pseudopodia ; nv. 

 nucleus. 



