116 THE EOSE. 



by animal external layers, are classed, with tlie Crowfoots, Crucifers, 

 Cranebills, &c., in the province of the Exogens.* It is a large and 

 important Order, including 71 genera and 1000 species, arranged in 

 several suborders (see Botanist and Florist, p. 101). They are chiefly 

 natives of the N. Temperate regions. Their prevailing property in 

 bark and root is astringency. Prussic acid occurs in the Almond and 

 Apple suborders. Many of the species produce edible fruits. 



The Peach tree {Amygdalas persica) is a native of Persia. The 

 Nectarine is a variety of the same species. In recent botanies it is 

 Prunus vulgaris. The Wild Plum of our own forests is Prmius 

 Americana. The Garden Plum (P. domestica) is a native of Europe. 

 The Cherries are also various species of Prunus. The Cherry Laurel 

 {P. Carolinidna), a beautiful evergreen tree of the S. States, has so 

 much prussic acid in its leaves and cherries as to render them 

 poisonous. The seed of the Peach is poison for the same reason. 



The Blackberry {Ruhus mllosus) is powerfully astringent. R. stri- 

 gosus is the delicious Raspberry ; R. occidentdlis, the Thimble-berry; 

 R. odor at us, the Mulberry. R. spectdbilis, the Shadberry, bears the 

 finest fruit in Oregon. 



The Attar of Roses, an essential oil of exceeding fragrance, is dis- 

 tilled from Rosa Damascena and R. moschdta. 20,000 flowers are 



* It will now be seen that from the leaf alone, or from the smallest fragment of it, 

 the place of a plant in the natxn-al system of classification can be determined. It is 

 the venation of the leaf that affords the criterion, and this pervades the fragment as 

 well as the whole. We have now considered three diverse modes or types, which are 

 severally characteristic of the three Grand Divisions of the Vegetable Kingdom. 

 First, the forked- venation of the Cryptogams, best seen in the Ferns (p. 21). Here the 

 veinlets divide and subdivide each into 2 smaller ones, which run on straight from 

 center to circumference— terminating in the margin or in a fruit-cluster, never re- 

 uniting when once parted. This is the simplest of all kinds of venation, and is pecu- 

 liar to the simplest of all plants which rise above the purely cellular Mosses, where 

 there are no veins at all. Second, the parallel-venation of the Flowering Eudogens, 

 seen in the Tulip, and the Grasses. Here the veins run parallel to each other on the 

 surface, without dividing or interlacing, so that the leaf may be torn from base to 

 apex regularly along the course of any of the veins. Such an arrangement of veins, 

 comparatively simple, is associated with flowers always ternate in their parts, seeds 

 always with one cotyledon in its embryo, and a stem without bark or annual woody 

 layers (p. 36). Thirdly, the netted-venation of the Flowering Exogens, just studied in 

 the Buttercups, and now seen in the Apple-tree. In such leaves the venation becomes 

 intricate. The veins divide to infinity and their ramifications reimite as often, form- 

 ing a network all through the leafy tissue, as beautifully illustrated in " skeleton 

 leaves." This, the highest type of venation, is associated with the highest develop- 

 ment of vegetable life-flowers many-parted, seeds with two cotyledons, and wood 

 /if any) wjth bark and annual layers. 



