THE SOUTHERN PLANTER. 



5-45. 



above. Where the evaporation was very 

 rapid the pressure was removed, and thus 

 no tension or gorging of the vessels or 

 soils could result. This evaporation is 

 important as connected with the influence 

 of excessive vegetation in modifying the 

 condition of roots. It is well know^n — it 

 is shown 'by the experiments, I think, of 

 most cultivators — that excessive develop- 

 ment of the foliage is unfavourable to the 

 development to the roots of plants in the 

 first instance. We have not only to con- 

 sider the different direction of the energy 

 of the plant, and the tendency of the 

 growth of the foliage itself, but I think 

 the rapid evaporation from the leaves may 

 cause too quick a flow of the sap through 

 the structure, and prevent that elaboration 

 which is necessary from taking place in 

 the roots. I think all our observations 

 hitherto tend to show that a certain amount 

 of elaboration does take place in the roots 

 themselves, and if there is too rapid a flow 

 of the nutriment absorbed by the roots 

 towards the upper part of the plant, there 

 is not a sufficient supply of elaborated 

 nourishment in the roots, and we get too 

 crude a condition of sap in the upper part. 

 Jn the cases of plants cultivated for their 

 flowers, we see excessive luxuriance of 

 foliage producing an indisposition to flower 

 and a throwing back of the whole growth. 

 The same thing occurs wherever we pro- 

 mote too great luxuriance of foliage in 

 grain plants, as when we stimulate wheat 

 by excess of nitrogenous manures. There 

 is too great a development of vegetative 

 structure, and the same supply of climatal 

 agency (heat, light) is incapable of thor- 

 oughly ripening the seeds. We see the 

 same in garden plants, where too rich a 

 soil prevents the plants from flowering. 

 Almost any common weeds if transplanted 

 in a garden will run away and produce 

 leaves, and perhaps flowers, but the seeds 

 will scarcely ripen ; and even with culti- 

 vated plants it is a common practice 

 among gardeners to prune the roots, to cut 

 off the supplies of nourishment, especially 

 by withholding water, and thus cause the 

 plant to turn upon itself as it were, and 

 elaborate its food rather than devote it to 

 the production of new tissues. 



The absorption of food by the roots is 

 concerned not only with water, but with 

 the most important of the materials out 

 of which vegetable structure is formed, 

 35 



namely, nitrogen. There is little doubt 

 that the greater part of the nitrogen con- 

 tained in plants is absorbed by their roots. 

 All experiments tend in this direction. 

 When I say that nitrogen is the most im- 

 portant of the substances absorbed by 

 plants, that is the conclusion derived from 

 both chemical and anatomical investiga- 

 tions into the structure of plants. I may 

 direct attention to a paper I published in 

 the last part of the Society's Journal for 

 evidence of the importance of nitroge- 

 nous substances, not only in the develop- 

 ment of the tissues, but in the formation 

 of the secretions or elaborated substances. 

 Not only does the examination of the 

 structures show this, but experiments with 

 manures also thoroughly prove it. That 

 nitrogen in excess will do mischief I have 

 already stated, because it will produce ex- 

 cessive growth and prevent proper elabo- 

 ration : but a certain amount of nitrogen 

 is necessary in order to convert what may 

 be called the wild plant into a tame one, 

 to produce that full development of struc- 

 ture which we consider necessary to the 

 perfection of the plant. The cultivated 

 plant has all its favourable characters more 

 fully developed than the wild plant through 

 this more abundant, supply of food, and 

 the most important of the stimuli in this 

 food is undoubtedly nitrogen. The recent 

 experiments of M. Boussingault on the 

 growth of plants with or without nitrogen, 

 and with and without phosphate of lime 

 in combination, are very interesting in 

 this respect. He grew sunflowers — 1st, 

 in a mixture of pounded brick and sand, 

 carefully purified : 2nd, in the same mix- 

 ture with nitrate of potash and phosphate 

 of lime added ; and 3rd, in the same brick 

 and sand mixture with carbonate of potash 

 and phosphate of lime (thus giving the 

 alkali and keeping out the nitrogenous 

 substances). The plants grown in brick- 

 dust and sand, after struggling through a 

 few weeks of vegetation, attained only a 

 height of six inches, and they produced a 

 flower about an inch across ; and the same 

 result, with but little difference, took 

 place where the plants were grown in the 

 same mixture with phosphate of lime and 

 carbonate of potash. The phosphate of 

 lime did not enable the plant to go beyond 

 this starved condition ; and when the 

 whole was analyzed, the plants were found 

 to contain little more nitrogen than was 



