The leaf of the strawberry is compound, that is, it does not, like the leaf of the nettle, consist of one expansion only, but of more than one. It is, however, simply compound. But a leaf dividing a second time, as we have been explaining, is decomposite or doubly compound; and if it divide thrice or oftener, it is a supradecomposite leaf.

When a petiole has a number of leaflets growing from its sides it forms a pinnate, or pinnated leaf, FOLIUM pinnatum (pinna, a wing or pinion, Lat.). The conjugate, bijugous, and trijugous leaves, for instance, are pinnate; and when there are more pairs of leaflets than in these, they may be expressed by describing the plant as being furnished foliis pinnatis quadrijugis, with pinnate leaves, consisting of four pairs of leaflets, quinquejugis, of five pairs, and so on.

If you examine a leaf of an ash-tree or of a rose, you will observe that its folioles are in pairs, except one at the end: this forms the FOLIUM imparipinnatum, or FOLIUM pinnatum cum impari, that is,

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pinnated, with an odd terminal leaflet. Fig. 47. (a) Sometimes a pinnated leaf ends in a tendril, and, of course, is a FOLIUM pinnatum cirrosum, Fig. 47. (b); and sometimes there is neither a tendril, Fig.47..

nor odd leaflet, and then it is a FOLIUM abruptepinnatum, an abruptly pinnate leaf. Fig. 48. (a) When, as in the ash, and rose, the leaflets are opposite to each other, the leaf is said to be oppositely pinnate, FOLIUM opposite-pinnatum; but when they stand alternately, it is a FOLIUM alternatim pinnatum, an alternately pinnate leaf. Fig. 47. (c) Fig. 48.

a

H

b

Sometimes the leaflets grow gradually smaller from the base to the end of the petiole. This is termed a decreasingly pinnate leaf, FOLIUM pinnatum foliolis decrescentibus. Fig. 48. (b)

93. The FOLIUM lyratopinnatum, or lyrato-pinnate leaf, must not be confounded with the FOLIUM impari pinnatum. A beginner might easily suppose (a) Fig. 49. to be a leaf of the latter description, for it certainly is pinnate, and with a terminal odd leaflet. The great size of the latter, however, and the leaflets being gradually smaller from top to bottom, give the lyrate form, and make the distinction.

94. FOLIUM interrupte-pinnatum, an interruptedly pinnate leaf. When between every larger pair of leaflets is placed a smaller pair, or more than one. Fig. 49. (b)

a

Fig. 49.

b

nate.

95. FOLIUM decursive-pinnatum, decursively pinWhen the leaflets are connected to each other by a leafy expansion running along the edge of the petiole.

96. FOLIUM articulate-pinnatum, jointedly pinnate. Fig. 50. (e)

When a petiole splits into two divisions, and

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each division forms a pinnated leaf, so that two leaves, instead of one, are formed from the same footstalk; it is a conjugately pinnate leaf; FOLIUM conjugatum pinnatum, Fig. 50. (f); in which (a) shows the petiole, (b) its division, (c) one pinnate leaf, (c) another.

We have seen that the digitate leaf consists of a number of folioles standing on the point of the leafstalk. In a similar way a number of pinnated leaves may stand on the extremity of a petiole, so as to form a digitate, and at the same time a pinnate leaf, FOLIUM digitatum pinnatum, that is, both digitate and pinnate. Fig. 51.

97. FOLIUM bipinnatum, a bipinnate, or doubly pinnate leaf.

98. FOLIUM tripinnatum, a tripinnate, or trebly pinnated leaf.

These terms are easily understood. The first is "when the common petiole has pinnate leaves on each side of it,"* Fig. 52. (a); the second, when the common petiole has bipinnate leaves on each side. Fig. 52. (b)

In both these figures (c) denotes the common petiole; and it is obvious that the leaves from its sides in the first figure are simply pinnated, and in the second bipinnate. The first is decomposite, the second supradecomposite, or thrice compound.

Having now considered the principal sorts of leaves, I shall make some general observations respecting them. And first, I wish to remark that though the anatomy and physiology of plants

* Martyn.