LEA 



345 



LEA 



tljey survive for twice or thrice that ] tuted of resinous and gummy matter, 

 period. These organs are generally ofl with carbonate and sulphate of lime. 



. a green colour. Light seems to have i It appears to be nearly the same iu all 

 a powerful influence in causing this, | plants. The quantity varies, however, 

 since if kept in the dark they become ] in every species, probably in every in- 

 of a pale yellow or even white hue, un- ) dividual, and is greatly influenced by 



'less uncombincd hydrogen is present, | the quantity of water applied to the 

 in which case they retain their verdure [ roots 



though light be absent. Hence their 

 etiolation would seem to arise from 

 their being unable to obtain this gas 

 under ordinary circumstances, except 

 when light is present. Now the only 



The transpiration of plants decreases 

 with that of the temperature to which 

 they are exposed, as well as with the 

 period of their growth. This explains 

 why the gardener finds that his plants 



source from which they can obtain hy- j do not require so much water in cold 

 drogen, is by decomposing water ; and , weather, nor during the time that 

 how light assists in the decomposition, i elapses between the fall of their blos- 

 may perhaps be explained by the dis- i soms and the ripening of their seed. 



oxygenizing power with which it is 

 gifted. The violet rays of the spectrum 

 have this power in the greatest degree ; 

 and Sennebier has ascertained by ex- 

 periment, that those rays have the 

 greatest influence in producing the 

 green colour of plants. 



When leaves are of any other hue 

 than green, they are said to be coloured. 

 This variegation is often considered to 



During this period they do not transpire 

 more than one-half so much as during 

 the period preceding and attending upon 

 their blooming. 



The transpiration takes place from 

 the upper surface of the leaves; and 

 if these gradually decay and fall, the 

 growth of the plant ceases until fresh 

 leaves are produced. Hence arises the 

 benefit which plants derive in rooms, 



be a symptom either of tenderness or | greenhouses, and other confined in- 



closures, from keeping those surfaces 

 cleansed with the sponge and syringe. 

 Some plants are particularly sensitive 

 to injury from any check to their tran- 

 spiration, among which are the tea- 

 scented roses; and it thence arises that 

 they cannot now be cultivated in nur- 

 sery-gardens near London, where they 

 once flourished when that metropolis 

 was less extensive. 



It must be remembered, however, in 

 using the sponge and syringe, that the 

 under side of leaves is an absorbing 

 surface, benefited by being kept clean, 

 and by the application of moisture. 



debility, and it is certain, when the 

 leaves of a plant become generally 

 white that that individual is seldom 

 long-lived. Mr. Knight, however, has 

 demonstrated that variegation is not a 

 certain indication of a deficiency of 

 hardihood. 



The function of the leaves appear to 

 be a combination of those of the lungs 

 and stomach of animals ; they not only 

 modify the food brought to them from 

 the roots, so as to fit it for increasing 

 the size of the parent plant, but they 

 also absorb nourishment from the atmo- 

 sphere. The sap, after elaboration in 



these organs, differs in every plant. The kidney bean, sunflower, cabbage 

 though as far as experiments have been and spinach, absorb moisture equally 



tried, it appears to be nearly the same 

 in all vegetables when it first arrives to 

 them. The power of a leaf to generate 

 sap is in proportion to its area of sur- 

 face, exposure to the light, and conge- 

 nial situation. 



Evergreens transpire less moisture 

 than deciduous plants, which would 

 lead to the expectation that they are 

 more capable of living in dry situations, 

 which in general is really the case. 

 The matter transpired by a healthy 

 plant is nearly pure water, .5.000 grains 

 of it never containing more than one 

 grain of solid matter, and this is consti- 



by their under and upper surfaces ; the 

 cockscomb, purple-leaved amaranth, 

 heliotrope, lilac, and balm, absorb most 

 freely by their upper surfaces ; and the 

 vine, pear, cherry, apricot, walnut, 

 mulberry, and rose, absorb most by 

 their under surfaces. 



The transpiration from the leaves of 

 plants is effected through pores or stro- 

 mates, varying in number and size in 

 every species, but being usually either 

 largest or most numerous in plants in- 

 habiting moist or shady localities. This 

 is a wise provision, for such plants, con- 

 sequently, have an abundant supply of 



