1326 



PHYSIOLOGY 



PHYSIOLOGY 



concerned in the conduction o£ t!ic ilif;tsted or leaf- 

 formed foods to other parts. 



Seed Production. — So far as we linow, the ultimate 

 function of a plant in nature is to produce seeds or to 

 reproduce its kind. It matters not how far the horti- 

 culturist may have diverted this natural function in 

 particular instances, in general the sum of the physi- 

 ological activities is directed to seed-production. Much 

 energy is directed to the development of form and color 

 in the flower, also of fragrance and odor, and there are 

 deep-seated physiological processes connected with pol- 

 len and ovule production, with pollination, fertilization 

 (see p. 579), and the subsequent development of the 

 seed. 



Seeds are, as a rule, richer in nitrogenous matter 

 than other parts of the plant. Likewise, in phosphorus 

 and magnesium salts there is a marked increase m the 

 seed. Of these last-named substances, there is a migra- 

 tion, as it were, from the older parts to the region of 

 seed formation, and finally to the seed On the other 

 hand, the salts of lime gradually increase in quantit\ in 

 the older tissues, particularlj in the old assimildtorj 



The Living Protoplasm the Seat of Vital Action.— 

 Physiological activities cannot be thoroughh studu il by 

 the use of the plant as a whole or bj the use iit the 

 organs as particular parts of a complex whiik The 

 final seat of all the plant activities resides m the living 

 protoplasm of the cells composing the plant. Excejit as 

 serving purely mechanical purposes, the old heart wood 

 and bark of trees are inactive, and they contain no liv- 

 ing substance. They are made niereh of the h.iidened 

 walls of cells which once constitutf d In in.,' puts The 

 actual living parts, such as thf b i\( ^ 1 u i^ flowi is, 

 fruits, and young wood, are compo^i I ..I In iii_ . . IN 1 lie 

 most essential part of a living ti II iv jln [ i. t< | I ism, a 

 semi-fluid, viscid substance which cuiistitiitLs tht Ining 

 material in all organisms. A defanite 1 1>* r ot the pro- 

 toplasm surrounds the inner surface of the cell wall, 

 and protoplasmic strands radiate throughout the cell, 

 in which is also differentiated a denser and absolutely 

 essential part termed the nucleus In addition the cell 

 contains an abundance of cell sap, or water, holding in 

 solution certain food substances. The cell wall is a 

 mechanical support, and as a ph> siological agent it is 

 quite dependent upon the protoplasm In conjunction 

 with the wall layer of protoplasm, the cell sap absorbs 

 water osmotically from weaker solutions outside, and by 

 the same process solutions are passrd fnmi cell to cell 

 and diffused throughout the growing |iiits Wlit-n ti ms 

 piration is proceeding it is some ot This w ii. t "t iIm < < II 

 sap which is given off through tli. I i\ s mt ihc ii 

 As a result of this loss of wati t tin ] i t | I i m . i n 

 tracts away from the cell wall and tl ■ ii^i.liu irm^ ii 

 of the cell is lost. Thus the ci IK ni.l ili. iissu.sl s, 

 strength, and the plant becomes Hi .id mil wilii il 



It is by means of the chlorii]ili\ 11 I m ii is n i \\, 

 chlorophyll alone which has to do wifh tin tuim itmn i t 

 starch from carbon dio\id. The chloriiph\ll is imlied 

 ded in the living substance, forming detinire chloroph\ II 

 bodies; and it is only when associated with living matter 

 that it can perform its functions 



The Plant h A" ' 1 ' , I ■ IP ' ' T' 



frritahl, .^Wlun 1 , i 



TliC i-cl.uiuu ul' ll.r (.l.ial I. 

 ulus, is one of the most pr 

 nature. In a dark chamber 

 young shoots will direct 

 themselves or grow directly 

 toward light admitted through 

 a small slit. Note how the 

 seedling bends toward the 

 light in Fig. 1788. If exposed, 

 the roots would dirnt tlieni 

 selves in i 

 E\en ther 

 plants will 

 the source of ligl 



1788. Youneseedhng showine 

 bcndine towards the light. 



be well (ibscrNed initsnli \\hiii tin sun is Inw i 

 any time of da> w ith i w iml w _ i I n \i n ii 1 1 



case of the resp i li_l t i i i I n I m il 



lettuce (Laitucu s wl i 1 i I n i i 



pass plant. In sunluht tins [ 1 mt li liis its 1. i\ 

 a vertical plane, ont rii« ot le^ues pointing iimt 

 the other south. This piovision may be to a\ end tl 

 rays of the midda> sun, and yet to secure the In 

 \.intige ot tilt hssinteiis, fmenoon and afternimi 

 sliii . 1 II I I I 1 1 ms to the stiniu 



be stimulated 



ipon all living pro- 



growth is incit 

 e.tisting cells, 

 the embryo dr 

 and is able to i- 

 tion into tissue 



has already occurred ^\ i is growth be- 



gins, the influences of s assert them- 



selves. The first shoot i i .diout in the 



soil, but, directly against il i i i .,1 i\it\ (mg.i 



tively attracted), it din ( ts Its, ii n| H II I In in 1 \ n th 

 contrary manner, the hrst 1 t iin 1 t..l li\ tlu siunnlus 

 of gravity (positively .ittii.ii.h .Im ts usi It di.wn 

 ward. Only the overthrow 01 om ili.iLuamg of gia\it\ 

 by some superior stimulus can pic\cnt this rtaition. 

 It a pot containing a seedling be jilaced upon its side, 

 the stem will actually curve when some growth has 



im may also b 

 more readily 1 

 r varieties or sp. 



t _i neral sanitar\ (oiiiliin us t. 1 1 | 1 mt 



^1 \ I I 111 ilisiiTpfion of wiiter b\ the root 



liMis tl in in it 1 tun . I St iichby thelea^es, tianspir.i- 

 II 11 m I III 1 1 n I s, s lie to a large extent depen- 

 di lit uiM II tin I. mill 1 uiii. Hot, dry winds of the suni- 

 iiui tiiiu (iliLU 1 ausi siiioiis miury to trees, owing to 

 the rapid transpiuition from the leaves. In dry seasons 

 this IS very likely to occur with the Norway maple 

 Fig. 1789 represents an in.piry of this kmd. As a rule. 



