FOREIGN NOTICES. 



337 



there is scarcely any indication of its existence. 

 At this time, if we oall in the microscope to our 

 aid, we shall find that, al the exterior line of d< - 

 mar cat ion, there Is simply an increased deposit in 



the cells composing tho bark, and a Very minute 

 passing from its inner surface. The line 

 of junction in the interior rarely presents any 

 change more marked than a larger deposit of 

 raphides or crystals there, than occurs elsewhere, 

 or occasionally a deposit of some dark resinous 

 material. Iodine, at this time, stains the whole 

 tissue yellow, and scarcely detects the existence 

 of a single granule of starch either in the leaf or 

 stem. At this time the leaves require considera- 

 ble force to separate them from the branches — so 

 much so, that we sometimes find that they bring 

 with them some of the wood from the parent 

 6tem; and if a branch is cut off and dried, the 

 leaves cannot be torn from their attachment with- 

 out great skill and management, showing that 

 the joint is not yet complete. By and by, how- 

 ever, a change begins to take pluce; with the ad- 

 vance of the season, or from some other cause 

 depending upon the situation and idiosyncrasy of 

 the plant, the line of demarcation becomes well 

 marked, and the eye can detect it throughout the 

 whole of its course, internally as well as exter- 

 nally. The microscope shows at the same time, 

 that the process of bark, which was at first ru- 

 dimentary, has gradually increased, and that an 

 evident change is taking place in the nature of 

 the cells which contain the raphides. Iodine now 

 tinges the proximal side of the junction a deeper 

 hue than the distal, and we begin, here and there 

 to see a blue dot, marking the existence of a 

 starchy mass. As the season advances, this 

 change becomes more apparent. The process of 

 bark increases perceptibly, till it reaches the 

 fibro- vascular bundles, when it receives a slight 

 check, but soon continues its progress until these 

 are nearly eaten through or absorbed, and the 

 prolongation of the epidermis has entirely cover- 

 ed the surface of the articulation. At the same 

 time (in the Poplar very distinctly, and in other 

 plants more obscurely), a great change is taking 

 place in the contents of the cells, on both sides of 

 this prolongation, in the formation of a large 

 quantity of starch, probably for the nutrition of 

 the young leaf-bud, when it begins to expand next 

 year. In the Poplar this deposit of starch takes 

 place in the bark and wood at the base of the 

 leaves to a great extent, so much so, that iodine 

 renders a section completely dark; and not only 

 at this spot, but for a short distance also on the 

 distal side of the joint. If we now make a sep- 

 aration of the base of the petiole and the stem 

 under the microscope, we '•hall find that the dis- 

 ruption takes place invariably through ihc ce 

 tissue, external to the' prolongation of the epid- 

 ermis, so that when it bus been effected, the tree 

 does not suffer from the effects of an open wound. 

 The change that takes placo in the cellular tissue 

 prior to its disruption, appears to me to be simply 



a sort of self-disintegration ) the cells contract 



and In me rounder, and separate their walls 



from each other, so as to destroy their cohesion. 

 J am very greatly inclined to think, from the 

 (ion of starch in their interior, that the 

 process is altogether a vital one; that it is, in 

 fact, the last act of life at the base of the petiole. 

 We are strengthened in the belief of the vita) 

 character of the act, when We consider that the 

 provision for the fall of the leaf, the formation of 

 the articulation, has been going on from the 

 earliest existence of the petiole, that it advances 

 with the growth of the leaf, and is not complete 

 until the leaf itself is of no more use. It must 

 be borne in mind too, that it is not necessary that 

 articulated leaves should be dead when they fall, 

 as we frequently find them lying upon the ground 

 green and apparently vigorous for a time; and il 

 we examine any of them that have fallen natural- 

 ly, we shall frequently, if not always, find that 

 the base of the petiole is plump, fresh, and appa- 

 rently living, which it would not be were its vi- 

 tality entirely gone. The provision for the sep- 

 aration being once complete, it requires little to 

 effect it ; a desiccation of one side of the leaf- 

 stalk, by causing an effort of torsion, will readily 

 break through the small remains of the fibro-vas- 

 cular bundles; or the increased size of the coming 

 leaf-bud will snap them; or if these causes are 

 not in operation, a gust of wind, a heavy shower, 

 or even the simple weight of the lamina, will be 

 enough to disrupt the small connections, and send 

 the suicidal member to its grave. Such is the 

 history of the fall of the leaf. We have found 

 that it is not an accidental occurrence, arising 

 simply from the vicissitudes of temperature and 

 the like, but a regular and vital process, which 

 commences with the first formation of the organ, 

 and is completed only when that is no longer use- 

 ful: and we cannot help admiring that wonderful 

 provision that heals the wound even before it is 

 absolutely made, and affords a covering from at- 

 mospheric changes before the part can be sub- 

 jected to them. In the Copper-Beech, and some 

 other trees whose leaves die sonic time before 

 they fall off, the development of the starch-bear- 

 ing cells on the distal side of the articulation does 

 not take place; nor is there that disruption or 

 disintegration of the cell-walls which is ordinarily 

 met with. The joint, however, consists of laxer 

 tissue, which is readily broken through by any ac- 

 cidental violence, such as wind and storms ol 

 rain, or by the growth of the new leaf at the 

 base of the petiole at the commencement of spring. 

 Botanical Gazette. 



Orchids from Seed. — I have read with inte- 

 resl the previous en Lunioations on the crossing 



and raising of Orchids from seed, which have ap- 



peared in pour pages, and, from what has oome 



under my notice, I have not the least doubt of the 

 practicability of the affair. Dendrobium nobile 

 crossed with D. chrysanthemum produced me a 



