PROPAGATION BY LEAVES. 



267 



a red and green colour ; vessels are seen to be produced and buds organised, 

 which, if placed in favourable circumstances, will evolve into shoots. I have 

 seen the buds literally crow^ded together like bees in a hive. Dr. Carpenter 

 says, that the blood of animals, even when altogether separated and spread 

 out, has been seen to organise vessels, from the strength of the vital principle." 

 This seems also to have been Mr. Knight's opinion. It is, however, of 

 less consequence to adopt either theory than to follow a practice which has 

 been found successful by cultivators, and which takes place in nature in the 

 leaves accidentally broken and left on moist soil of cardamine hirsuta, the 

 common water -grass, sedums, and other succulent -leaved plants, and 

 probably various others, independently of those which root by the leaves 

 in consequence of these producing bulbs, as in the case of Woodwardza 

 radicans (608). 



610. The conditions generally required for rooting leaves are, that the leaf 

 be nearly full grown ; that it be taken off with the petiole entire ; that the 

 petiole be inserted from an eighth to half an inch, according to its length, 

 thickness, and texture, in sandy loam, or in pure sand on a stratum of rich soil; 

 and that both the soil and the atmosphere be kept uniformly moist, and at 

 a higher temperature than is required for rooted plants of the same species. 

 The leaves of such succulents as cacalia, crassula, cotyledon, kalankoe, por- 

 tulaca, sedum, sempervivum, cactus, and similar plants, root when laid on 

 the surface of soil, with the upper side to the light, and the soil and atmo- 

 sphere is kept sufficiently close, moist, and warm. The first change that 

 takes place is the formation of a callosity at the base of the petiole ; after 

 which, at the end of a period, which varies greatly in different plants, roots 

 are produced, and eventually, at an equally varying period, a bud from 

 which a leafy axis is developed. M. Pepin states that rooted leaves of Hoya 

 camosa, and those of several kmds of Aloe, did not produce a bud till after 

 the lapse of ten or twelve years. The leaves before they emit roots must 

 be slightly shaded to prevent excessive perspiration during sunshine, but 

 afterwards they may be fully exposed to the light. 



611. Rooting portions of leaves. It appears that some leaves will throw 

 down roots with only a part of the petiole attached, and that others 

 will even root from the mid-rib when the leaf is cut through. In 1839, 

 M. Neuman, of the Paris Garden, seeing the theophrasta latifolia (Clavija 

 omata, D. Don^ growing so well from cuttings of leaves, conceived the 

 idea of cutting several of them in two, and treating them in the same 

 manner as entire leaves. Accordingly, he cut a leaf in two, and planted 

 both parts in the same pot, treating them exactly alike. In about three 

 months, the lower half of the leaf (fig. 178) had made roots, but the upper 

 half had none ; though, some time afterwards, when it became necessary 

 to separate the cuttings, M. Neuman found that the upper part of the 

 leaf had also made roots (fig. 179), but that these roots were much shorter 

 than those of the lower half. The rooting of the two halves of a leaf of the 

 theophrasta, so hard and dry as every one knows these leaves to be, appearing 

 to him an interesting circumstance, he continued to pay attention to them for 

 six months. He wished to ascertain if they would produce buds as in other 

 cases, for he was in hopes they would, as he remarked that the roots increased 

 in the pot. At last in the seventh month, for the first time, he saw at the 

 extremity of his two half leaves, buds appearing, as well formed as those pro- 

 ceeding from the base of the petiole of an entire leaf. In June, 1840, these two 



