PBELIMINARY DISCOURSES. XlX 



the starting points from which those organs are evolved, during the 

 growth of the plant.* Even the stem of the embryo plant, as it exists 

 in the seed, has its nodes, with the first of which the cotyledons 

 are connected, and at the next above, we find those minute expan- 

 sions known by the name of primordial leaves. The internode*, or 

 spaces between those little knots in the stem, may be long, or 

 short, which will, of course, determine the distance between the 

 leaves. They may be so short as scarcely to be perceptible, in 

 which case the leaves will necessarily be brought close together, in 

 tufts or bunches ; or they may even be wholly suppressed, as it is 

 termed, so as to reduce the leaves to the same plane ; either in 

 opposite pairs, if but turn are developed, or in vchorls of the normal 

 number in the circuit of the stem, if all are developed. If the nodes 

 are scattered, or disposed in a spiral line, the leaves, of course, will 

 be arranged in the same order, on the stem and branches. Thus we 

 are furnished with a key to the whole mystery of the arrangement of 

 leaves and buds, and consequently, of the branches, which arise 

 from the buds. We shall now be prepared to watch the development 

 of the foliaceous appendages of the plant, and the successive changes 

 of their form and character, as the stem ascends. The cotyledons (in 

 that large division of the vegetable kingdom which is provided with 

 two of those organs,) are always opposite, as likewise are, for the 

 most part, the next pair of leaves called primordial : but the suc- 

 ceeding ones are variously arranged, in different families either 

 alternate, opposite, or vtrticillate. The leaves on the stem, and 

 branches, usually differ in form, also, from those early rudimentai 

 leaves which appear at germination. If the plant is duly nourished, 

 the leaves are apt to be well developed until it has reached its 

 destined height or is sufficiently matured far flowering, when they 

 usually become smaller. In several natural families, there are 

 foliaceous appendages, or accompaniments, at the base of the leaves, 

 or petioles, which seem to be a sort of exuberant growth, or super- 

 numerary products : these are called stipules. 



In sterile, or ungenial soils, the leafy expansions are less com- 

 plete, and are liable to modifications which appear to be the acci- 

 dental result of defective nourishment, though they often become 

 fixed, and permanently characteristic. Prof. DE CANDOLLE terms 



* Sometimes the bud instead of being in the axil of the leaf, as is usual is 

 formed and situated directly under, and within, the base of (he petiok ; in which 

 case, consequently, the hollow base of the petiole covers the bud, as an extin- 

 guisher does the stump of a candle. This feature is well exhibited, in autumn, 

 by the Buttonwood Tree (Platanus); and may be likewise observed in the common 

 petioles of the Bhus, the Rdbinia, and the Cladrattis (or Virgilia). 



