For Junuury, 1922 



13 



containing mineral salts in solution necessary for the 

 life of the plant. I>"or the latter purpose the roots have 

 innumerable tiny hairs just behind the growing tip capa- 

 ble of absorbing moisture through their cell walls. The 

 water, containing mineral salts in solution, is transferred 

 from cell to cell until the conducting tissues of the root 

 are reached. From here they are taken to all parts of 

 the plant, especially to the leaves, where, in the presence 

 of chloro]>hyll, carbon is taken from the air and mixed 

 with the water and salts and thus organic matter is pro- 

 duced in sunlight. Without the chlorophyll found in the 

 leaves, the plant can not utilize the mineral salts in solu- 

 tion of the soil waters. 



The young seedling which we have jusl left through 

 this necessary digression, as it was about to bore its 

 roots into the ground, can not use the salts absorbed 

 with the moisture for the production of food. But 

 growth is not possible without the assimilation of food. 

 Therefore it utilizes the cotyledons and draws its food 

 from them until the first pair of leaves have been fullv 



tinishcd organic [jroducls arc led In ihc \ari(iiis parts 

 of the plant. All surphis water evapor;itcs iliniu^h ihe 

 stomata. 



The entire plant consists of ;i series of carbonaceous 

 jiroducts which it has produced but which do not all 

 consist of carbon dioxide and water alone. In the green 

 chlorophyll containing tissues oi the leaves, carbon 

 dioxide from the air and water from the soil produce 

 formic acid, an organic substance, and during its manu- 

 facture free oxygen is given off as a waste product. 

 Further transformation takes place: the formic acid is 

 changed to formaldehyde and more free oxygen is pro- 

 duced. I'inally grape sugar is manuf;ictured. This pro- 

 cedure is dejjendent upon a sufficient quantity of day- 

 light, and does not take ])lace at night, lint Ihe first 

 tangible product produced is starch which is found about 

 the grains of chlorophyll. This starch is the most im- 

 portant product, and from it, the plant does, with the 

 aid of other salts, produce nearly all other plant materials. 

 The most essential are the carbohvdrates, sugar and 



10 



t 



A day later the first /ruiv.? bc;^in to 

 unfold. 



Tlw next day the leaves are unfolded. 



One day later the new shoot has 

 begun its devejoptnent. 



developed. Now an uninterrupted stream of water passes 

 through the plant from the roots to the leaves, which 

 is then manufactured into food material with the aid 

 of soil salts. 



The explanation for the rise of the sap is complicated. 

 It is not dependent upon any one factor but upon many. 

 Some of the more important are the transpiration or 

 evaporation from the leaves which causes the water to 

 rise in the conducting tissues, /. c. it pulls the water up- 

 ward, the osmotic pressure of the roots which 

 forces the water upward, also the diffusion of liquids and 

 the turgidity of the cell which have their effect. Then 

 there is the imbibing and absorption of liquids through 

 the various membranes of the cell, and the capillary at- 

 traction which plays a far greater part than is supposed 

 since the conducting tubes are microscopically thin. 

 There is also the cohesive force of water which, in a very 

 thin tube, as experiments have shown, is excessively 

 large, hundreds of pounds' pull being necessary to force 

 the hairlike column of water apart, etc. The sap, when 

 it arrives in the leaves, is manufactured with the aid of 

 chlorophvll and the carbon dioxide of the air into organic 

 material which is used by the plant for the purpose of 

 reconstructing and building up of new tissues. These 



cellulose, then the fats, and finally proteids of which 

 asparagine, especially found in asparagus, is the most 

 important. These three groups are sufficient for the 

 production of all plant organisms. 



The wanderings of the products manufactured in the 

 leaves and in other places to those places where they 

 are either stored or used is most complex as the plants 

 do not have an open circulation and transportation sys- 

 tem. Transportation must proceed through those closed 

 cells which only too often close the conducting tissues. 



The only place where the translocation of substances 

 can be directly observed is in the leaf and the only 

 substance which can be observed is starch. In order that 

 it may be transported from one place to another it must 

 first be prepared for its journey, which is accomplished 

 through enzymes. These are peculiar substances with 

 only partly known chemical composition and having the 

 property of transforming large quantities of material into 

 a soluble form, that can pass through the well wall. This 

 soluble material is changed back again to starch after it 

 has passed through the wall, thus disturbing the equilib- 

 rium of the surrounding cells which then pass more 

 sugar into this cell. Therefore the starch is not carried 

 {Continued on page 17) 



