134 



HISTORY OF THE VEGETABLE KINGDOM. 



among the various classes and species of vegeta- 

 bles as among animals. Thus some plants are 

 annuals, and last for one season only, springing up 

 suddenly from seed, coming rapidly to maturity, 

 reproducing other seeds, and scattering them 

 abroad into the soil, and after this immediately 

 perishing. Such is the case with the various 

 kinds of com, as oats, wheat, and barley. Some 

 plants continue to live for a period of two years, 

 and are therefore called biennials, springing up 

 the first year fi-om seed, and producing root and 

 leaves, but no fruit ; and in the second year pro- 

 ducing both flower and fruit, as the carrot, pars- 

 nip, carroway. Other plants are perennial, last- 

 ing for many years, of which some are called 

 under shrubs, and die down to the root every 

 year; others are called shrubs, and are perma- 

 nent both by the root and stem, but do not at- 

 tain to a great height or great age ; others are 

 called trees, and are not only permanent by both 

 root and stem, but attain to a great size, and live 

 to a great age. The oak, in particular, is re- 

 markable for its size and longevity, taking at 

 least one hundred years to attain its full growth, 

 and continuing vigorous for one or two hundred 

 years more before falling to decay. But even 

 of plants that are woody and perennial, there are 

 parts which perish annually, or which are, at 

 least, annually separated from the individual, 

 such as the leaves, flowers, and fruit, leaving no- 

 thing behind but the bare caudex, which sub- 

 mits in its turn to the ravages of time. Hence 

 we shall consider first the decay of the temporary 

 organs, and next the permanent organs, and con- 

 sequent death of the whole plant. 



The decay of the temporary organs, which 

 takes place annually, is a circumstance familiar 

 to every one, and comprehends the fall of the 

 leaf, the fall of the flower, and of the fruit. The 

 fall of the leaf commences in most plants in this 

 climate with the first chill of autumn, and is ac- 

 celerated by the fi-osts of the coming winter, that 

 strip the forests of their foliage, and the face of 

 nature of its green verdure. Yet there are some 

 trees that retain their foliage throughout the 

 whole winter, though changed to a dull and 

 dusky brown, as the beech tree and others, that 

 retain them in full verdure till the ensuing 

 spring, when they ultimately fall. These latter 

 are known as evergreens. It was at one time, 

 indeed, a common error, and perhaps it continues 

 to be so to some extent still, that evergreens 

 never part with their leaves. This error may be 

 traced back even to the period of the fabulous 

 history of the Greeks, with whose mythology it 

 was closely interwoven, at least in one particular 

 example, as related by Theophrastus, who says 

 that in the country of Cortynia in Crete, it was re- 

 ported there was a plane tree growing by a foun- 

 tain which never shed its leaves, being the tree 

 under the shade of which Jupiter is said to have 



had his interview with Europa. But Theophra.s- 

 tus was himself acquainted with the fact of the fall 

 of the leaves of evergreens, as every accurate ob- 

 server of nature must be, though they do not ac- 

 tually fall till the young leaves have begun to 

 appear, so that trees of this sort are never left 

 wholly witliout leaves, which it was hence sup- 

 posed they never shed. In warm climates it is 

 said that many plants retain their leaves for 

 several years; but in temperate and polar cli- 

 mates there are no such plants to be found. 



Such is the fact of the annual fall of the leaves. 

 But the cause of their fall has been an inquiry 

 which has baffled the attempts of the botanist 

 to explain. Du Hamel minutely considered this 

 subject without arriving at any very definite 

 conclusion. He observed that leaves which fall 

 the soonest transpire the most, and are conse- 

 quently the soonest exhausted, and rendered un- 

 fit to discharge their functions, so that the period 

 of the fall of the leaves of difl^erent species is pro- 

 bably in proportion to their capacity for tran- 

 spiration. Their fall is accelerated by frost or ex- 

 cessive heat, followed by rain. It is also acceler- 

 ated, if not actually induced, by the sti-ucture of 

 the pedicle, which is very different from that of 

 the branch, having no prolongation of pith, and 

 nothing analogous in its mode of insertion, nor 

 in its external figure, which is divisible into an 

 upper and under surface, resembling the figure 

 of the leaf. He compares the union of the leaf 

 and stem to that of the joints of the lime twig, 

 which, at a certain period of its growth, are 

 stronger than its interaodia, but which really 

 give way after a frost. The comparison, however, 

 throws but little light on the subject, as the il- 

 lustration is itself to the full as dark as the thing 

 to be illustrated ; but he offers an additional con- 

 jecture, which is considerably more luminous. 

 When the sap begins to flow less plentifully, the 

 leaves, to whose vigour a great supply is neces- 

 sary, soon become dry, and consequently less fit 

 to convey it. But it is known that the branches 

 grow in thickness after they have ceased to grow 

 in length, which must necessarily occasion, in 

 some degree, a disruption of the fibres of the foot 

 stalk and stem, a branch at the point of articula- 

 tion, and hence the leaf loses its hold and falls. 

 This is certainly a very plausible conjecture, 

 though it may be doubted whether this explica- 

 tion will apply to the case of evergreens or of 

 plants in warm climates, that retain their leaves 

 for several years. It is not, therefore, altogether 

 satisfactory, and hence, accordingly, other expla- 

 nations have been offered. That of Willdenow 

 is as follows : As the sap is conveyed to the leaves 

 in greater abundance during the summer, the 

 vessels of the petiola become gradually more 

 woody, as well as the whole of the leaf. The 

 sap consequently stagnates, and at last the bond 

 of union between the leaf and stem is dried up 



