AUGUST. 235 



CLEAN LEAVES NECESSARY TO GOOD CULTIVATION. 

 With what feelings of delight does the country-born citizen view the 

 bursting buds and newly- developed leaves of spring in his Httle to\\Ti 

 garden! From their fresh green colour, as they unfold themselves for 

 the first time to the morning sun, he can just catch a gUmpse of Nature 

 as he was wont to find her in rural retreats of younger days. His 

 pleasurable feelings are, however, alas, but short-lived ; those leaves, 

 which but a week or two before were so verdant, so full of sweet 

 reminiscences, and so promising for the future, are already soiled and 

 uninviting. They now but faintly shadow forth the beauty and freshness 

 of rusticity, and fail to afford those enlivening and cheering emotions 

 which they did when they first broke through their winter coverings. 

 Now more than ever did he long for some suitable protection from the 

 impurities of a smoke-loaded atmosphere, and it was fortunately no 

 great while before his desires were gratified ; for the duty coming off 

 glass placed that material within his reach, and the most delicate and 

 choice of his Httle favourites soon smiled under an elegant transparent 

 roof Difficulties in the way of successful cultivation, however, still 

 presented themselves. He could not give air, but the atmosphere 

 inside became loaded with soot and dust ; the pores of vegetation got 

 choked up, and many were the " sear and yellow leaf" he picked off. 

 This continued, together with the blighting influence of the atmosphere, 

 which could not be altogether excluded, soon brought his plants into 

 ill health, and, as a last resource, he thought he would try the effect of 

 keeping the foliage constantly in a perfectly clean state by means of 

 washing it frequently with soap and water. This was found to act 

 like a charm. The plants soon began to improve as much in health 

 as they pre\nously got out of it, and this from the employment of no 

 other agents than those just mentioned. Nor is this to be wondered at, 

 when we consider the very important part leaves have to play in the 

 economy of nature. Even the exhalation from them in a given time is 

 remarkable. A French writer recently made a series of experiments 

 on this subject, by enclosing a living leaf between two bell jars, one 

 applied to the upper and the other to the under surface, and ascertain- 

 ing the quantity of fluid exhaled by means of chloride of calcium, which 

 absorbs water with great rapidity. He found that the exhalation fi-om 

 the lower surface of the leaf was usually double, and even triple or 

 quadruple that of the upper surface. The same results were obtained 

 even when the leaf was reversed. The quantity of water exhaled has a 

 relation to the number of stomata or pores. The exhalation is greater 

 at the line of the ribs, or at the part of the epidermis or skin where 

 there is least fatty or waxy matter. The secretion of this matter in 

 abundance during the warm days of summer may tend to prevent the 

 plants being injured by rain and by the heat of the sun. By impedino- 

 exhalation, it tends to retain the moisture which is necessary for the 

 functions of the leaves. 



The difference of the exhalation is seen in the following table, in 

 which leaves of the same plant were exposed to the air, some of them 



