Page:An introduction to physiological and systematical botany (1st edition).djvu/87

Rh, and the means of increase, from the leaf above it.

By the above view of the vegetable œconomy, it appears that the vascular system of plants is strictly annual. This, of course, is admitted in herbaceous plants, the existence of whose stems, and often of the whole individual, is limited to one season; but it is no less true with regard to trees. The layer of alburnum on the one hand is added to the wood, and the liber, or inner layer of the bark, is on the other annexed to the layers formed in preceding seasons, and neither have any share in the process of vegetation for the year ensuing. Still, as they continue for a long time to be living bodies, and help to perfect, if not to form, secretions, they must receive some portion of nourishment from those more active parts which have taken up their late functions.

There is a tribe of plants called monocotyledones, characterized by having only one lobe to the seed, whose growth requires particular mention. To these belongs the natural order of Palms, which being the most lofty, and, in some instances, the most long-lived