PHYSIOLOUY 



An unfailing test for starch is a blue or blue-black 

 reaction on the addition of a weak solution of iodine. A 

 bit of starch paste, or the cut surface of a potato or 

 other starchy area, will i|\n.-kly sh..« iliis rr;i.'iiiiu. In 

 green leaves starch ni: 



chlorophyll in al'"lM'l 

 with iodine. In the same w 

 gated with white. The ki' 

 leaf alone will show starch 

 blue or purplish coloratio 

 have formed no starch. 



;mi.I III. ri -t;,llil.,L' ill.- leaf 



yoii.-rM,i,iiH.-s a Iriitvarie- 

 feli i»r ciilur.^il pali.s of the 

 the white areas showing no 

 1, demonstrating that they 



Fig. 



a irlass apparatus, such as is suo 

 1. iiH.ii-trute that a land plant cannot form 

 iini -],li, ic free of carbon dioxid. Over a 

 small p.'iiiil |>l,nii ii>r better, the plant maybe trans- 

 planted lo a irkiss jar protected at the top by rubber 

 cloth) is i>laced the vessel a, cemented to the glass 

 plate, 6. A solution of caustic potash in c absorbs the 

 carbon dioxid in the vessel, and all air admitted must 



shim- for a IVw days will show no starch 

 1 ti'siiiii; iis I. avis." In a short time it will 

 also become luiliialiiiv ami i-i asp to erow. 



Not only does chlurupliyll art in ,-.,i,iiii 

 light for the manufacture of ^i n. i,, 

 sunlight is absolutely necessary 111 ■ 

 may be normally developed, s 



darkened vessel or potato spmui^ \,Iip h i,:,,, pushed 

 into growth in a darkened cellar will remain yellow or 

 white. Moreover, the plants will grow long and slender, 

 and death will result when the plantlet can no longer 

 draw upon the parent part for stan-Iiy matters. The 



th sun- 



n.'phyli 



total dry weight of : 

 the dry weight of tin 

 connection it might 1 

 some li^ht in order t 

 the genninalion ..f ..r 



ight. 



terred 



I . «hi.h .starch is converted for translo- 

 d:uii in the leaves; and it is also trans- 

 ivin- ).arts of the plant, along with other 

 organic products, besiiles the various salts in solution 

 which have come up to the leaves from the soil. Under 

 the influence of the active protoplasm of the leaf-cells 

 or of other tissues, more complex compounds necessary 

 in t'r">"i nin !" r.iiined. All parts of the ordinary 

 plant .1 ' ■ upon the roots for a supply of the 



minii .: nnrogen; but, on the other hand, 



they an .;,:,;.,. > i ( h iident upon the leaves for the iirst 

 organu; .-.uIj-uuilu, and for much prepared food. 



Growth, ami Die Differentiation of Structure. -Plant 

 growth is apparent to the unaided eye as change in 

 form and size of orirans and tissues. The real evi- 



dence of growth is in the multiplication of the tissue 

 cells, or of constructive changes in the form and bulk 

 of these cells, (trowth may be so rapid that it may be 

 readily measured, or it may proceed so slowly or bj" such 

 obscure internal modifications that very little external 

 indication of the complex processes will be manifest. 



PHYiSlOLOGY 1325 



Even under such adverse conditions as that of decidu- 

 ous trees in w inter, some slight growth may be taking 

 place, and it is not well to dis^oi late from the idea of a 

 living plant all growth I'll n m. n i \i \ . itln li ss sieds 

 and other air-drii d I 1 m | n iiii\ Im " M limit glow Ih 

 for considerable jn 1 1 1 



Thegiowth 111 I I I I I li t liil iMit plant or 



.lust bai I ' 1 1 



the 



^liow growth through- 

 1 inndition of a beech 

 hd the long, delicate, 

 le very evident. Each 

 ^ readily seen in the 

 ; the delicate scales 

 oiii one another, each 



node 



the 



distinct joint 



stages of this general elongation are evident from 

 Fig. 1786. Finally as the branch lengthens through- 

 out its entire extent, the scales drop, the leaves expand, 

 the older nodes cease to elongate, and the wave of elon- 

 gation follows a few nodes behind the terminal bud. 



In the common woody plants growth in diameter is 

 accomplished by means of a distinct but thin layer of 

 tissue functioning as the zone of cell division, or cam- 

 bium. The cambium is located just between the wood 

 and bark. In fact, it divides a complete ring of fibro- 

 vascular bundles into an inner or woody portion ( xylem ) 

 and an outer or bast and sieve-tube portion (phloem). 

 Each year it gives ri.se on the inner side to a layer of 

 wood and on the outer side to a layer of bark, thus each 

 year covering up and pushing to the center, as it were, 

 the old wood, and pushing outward the old bark as a 

 protective covering. By this process the inner wood 

 retains its former dimensions, but the bark must con- 

 stantly expand to cover the increasing diameter of the 

 tree, and so it breaks into rifts and ridges of various 

 forms, or else peels off periodically. The differentiation 

 of the tissues in different parts denotes different physi- 

 ological functions. Thus the woody part of the young 

 rings conducts the water and other soil foods, and 

 through the woody bundles of the leaf-.stalk, veins, and 

 veinlets it is distributed throughout the plant body. 

 The bark or phloem portion of the bundles is largely 



