508 London Horticultural Society and Garden. 



Endogenous and Exogenous Trees. — After briefly recapitulating the heads 

 of his former lecture, Mr. Lindley observed that the principle of adhesion 

 may be termed the hinge of vegetable structure, since, perhaps, no other 

 science exhibits in a more striking manner its effects. Besides its regular 

 operations, this principle often produces monstrosities ; two gourds, two 

 apples, or two peaches, growing close together, become united from 

 pressing constantly against each other. The flowers of the cockscomb 

 owe their singular shape to this principle, as, in cases where it has been 

 prevented from acting, they have been found to spread out into branches. 

 A similar monstrosity has been observed in the common asparagus ; and in 

 several other plants. 



Every plant is covered, except at the extreme points of its roots and 

 the upper surface of its stigma, with a membrane or cuticle, which, though 

 so extremely thin and fine as to be generally invisible to the naked eye, 

 is yet composed of parts adhering so firmly to each other as to admit of 

 its being peeled off. When viewed through a powerful microscope, this 

 membrane is found to consist of cellular tissue studded with |$omata ; and 

 to appear streaked with a number of parallel lines, formed of rectangular 

 -or irregular network. 



Every seed contains within itself a vital point, or axis, consisting of 

 two cones, which, in the process of germination, elongate themselves in 

 opposite directions; one producing the stem, and the other the root. 

 These two parts being essential to all plants, Mr. Lindley proposed to 

 consider them separately. 



All stems, whether of herbaceous plants or timber trees, are subject to 

 the same general laws, and are all provided with leaf buds, by which only 

 varieties can be propagated. Buds are sometimes considered in the 

 nature of seeds, as they also possess a vital point from which both a stem 

 and a root will proceed ; but there is this essential difference between 

 them, that from the one is raised a new plant of the parent tree, and from 

 the other a distinct individual. Leaf buds spring from nodes, or knots, 

 of which there are always several on every branch, at regular intervals. 

 Sometimes these nodes are placed exactly opposite to each other, and at 

 others at various distances, but always on alternate sides of the stem. 

 Whenever two leaves are found together on the same side, without one 

 occurring on the opposite side, it may be safely concluded that the missing 

 leaf has been removed by some accidental circumstance. The spaces be- 

 tween the nodes are called internodes, and these intervals are of irregular 

 length ; generally, however, becoming shorter towards the extremity of the 

 branch. Buds are sometimes found on the internodes, but, when they 

 are, the circumstance must be considered as a kind of lusus nacurae, and 

 not as a general law. 



Each leaf forms with the stem an axil, in which is found an axillary 

 bud. Buds are covered with seales, generally dry and brown, which 

 drop off as the leaves unfold themselves. There is sometimes a second, 

 and even a third and fourth, set of scales, of various tinges of white, brown, 

 and red, found enveloping the incipient leaves. All, however, no sooner 

 expand, than they drop off. 



Buds are sometimes found upon leaves. The fragments of a leaf of a 

 species of Ornithogalum, laid upon moist ground, produced buds, not only 

 on the edge of the leaf, but on its surface ; and a few plants produce buds 

 on their leaves naturally. Among these may be mentioned the Malaxis 

 paludosa, and the Bryophyllum calycinum. 



Plants are divided into two classes, with regard to the internal structure 

 of the stem : viz., the endogenous, or such as increase inwardly ; and the 

 exogenous, or such as increase outwardly. The former do not enlarge 

 their bark, or outer circumference, after a certain point, but gradually fill 

 up their interior by successive depositions of fibrous matter, which, in the 



