1324 



PHYSIOLOGY 



green wDod, jincl often as much as 'J5 per cent in tlie 

 pumpkin. 



The rood Supply of Salts from the So«.- Besides se- 

 curing from the soil its water supply, the plant must 

 secure in the same way all of its ash constituents, and 

 usually all of its nitrogen, as soluble salts. The salts 

 furnishing food are such well-known food ingredients, 

 or constituents of fertilizers, as potash compounds. 



eed from the tu- 

 '■ bacteria. 



phosphates, nitrates, etc. The various mineral elements 

 generally necessary for the plant are potassium, phos- 

 phorus, sulfur, calcium, magnesium, and iron in small 

 quantities. These, a-* wfll ms othfr incs'-piifinl eli'mriit-;. 

 are the constituent-^ i hni nni.nn in tin' f.irni ..f ;isli wImii 

 the plant is bunitMl m ;iir. 'i'liai i:irii oim' of (iirvr ,-\r 

 nients, as well a^ niir-i.^.n, i < ii.-i'i'^~arv (.■!• liir lull 

 development of iin' liiuln r plant has ijirii it-p. attally 

 demonstrated. For this demonstration seedlings art- 

 supported and grown in ,iars containing culture solu- 

 tions. One or more of the above elements may be left 

 out in certain cases to be compared with one in which 

 all are present, and it will then be found that growth 

 and development will soon be arrested where even one 

 necessary element is entirely absent. 



Tfitrogen Sometimes Jf^uj-nished hy fht" .1 /'*•. — Plants 

 ordinarily get their nitrogen frnni tlm - ,il a^ n-T at.- of 

 soda, saltpeter, or other solnMc- ^::li I ' i ■' rule, 

 and although the air contains al.oiii ; ,, i , ■, i . ii,'ht 



of the free gas nitrogen, it is iir tin- i : a. . i,, u . , , inert 

 to most plants. Leguminous I'Umt - i Ja -umino-a ; form 

 a great exception to this rule. On tlie roots of such 

 plants are found swellings or tubercles, as in Fig. 1781, 

 caused by the growth of parasitic bacteria. By the aid 

 of these bacteria, the plant is altle to appropriate the 

 free nitrogen of the atmosphere ami to tlirivi- in a soil 

 almost free of nitrates. This htis l,c en .leni. initialed 

 repeatedly with plants in sand or water eultnia s. riiliz- 

 ing the free nitrogen of the air, legntninous (■roi)s. 

 whether used as green manure or not, restore the land 

 by returning to it more nitrogen than is taken away. 

 They necessarily enter into any thorough system of 

 rotation upon weak lands, and represent an important 

 economic factor in horticulture, particularly in orchard 

 culture. 



The Association of Hoots with Fungi. — Other plants 

 are also aided by an association of the root with certain 

 filamentous fungi. In connection with the roots of the 

 oak, beech and other woody as well as herbaceous 

 plants, this association of root and fungus (termed 

 mycorhiza) is of much aid in the ab.sorption of .solu- 

 tions from the soil. In such cases it is thought that the 



PHY'SIOLOGY 



fullest development of the plant is dependent upon the 

 presence of the fungus. 



The Formation of Organic Substance. — Next to the 

 elements of water (hydrogen and oxygen) carbon forms 

 the bulk of the plant substance. It is a constituent of 

 all starchy, sugary or nitrogenous (organic) products, 

 and of all woody fiber. It is, in fact, the eiennut u In.so 

 presence indicates organic substances. \\ Inn plants 

 are burned in an atmosphere more or I, -^ cl,.\,.i,| ,,( 

 o.\ygen, the bulk of the remaining eliairoal i- |.nie 

 carbon, for the ash present would be su small in \ oUinie 

 that it might be neglected. The ordinary green jilant 

 obtains this carbon only from the carbondioxid of the 

 titinosphere. Carbon dioxid forms onlv .04 to .O.'i percent 



able 



gVil\ 



uditions, h' 



carbon dioxid depends 

 and sunlight. The green .li! , i iK 



siderable part of the rays oi i , ! n 



of the energy thus provideW rail ..d .i ;. 



forced to unite with a portion .i :\v 



(HaO). Theunionof these siiii-taiM 

 by an ob.scure process, but in sinli a iv ■ i, i . 

 carbon and the elements of water i ti\,lri. 

 oxygen) are united in the form of a enli. 

 This substance is first readily demonsi laMe a 

 — of the composition CeHioOj. In tliis \ir 

 union, or synthesis, there is an excess of oxy 

 nished, and it is this oxygen which is throw 

 llie li-aves. Tliis process of uniting carbon di. 

 water niuler the intlmni.-e of ehlornphyll .and 



oil'; in the latter, a 

 tantly absorbed ami - 

 the ordinary plant 



very rapidly in sni 



a small amount o 



day a large amount 



The starch made 



to a soluble - 

 may then be 

 complex or^'.a 

 the sugar ni 



sported to some storage organ 



of the plant, such as root (dahlia), stem (potato), or 

 thickened leaf, and there be reconverted to starch or 

 changed to some insoluble or more complex product. 

 This translocation of the starch formed in the leaves 

 by day may be so thoroughly effected during a single 

 night that none will remain as starch by the next day. 



