56 ON LEAVES. 



The fifth clsss has simple ribs, proceeding from the base 

 to the extremity of the leaf; corn, grasses, and all the 

 gramineous tribe are comprised within it. These leaves 

 are always sessile. 



The contour, or external form of the leaf, is of much 

 less importance than the direction of its ribs. The in- 

 dentures, or teeth of leaves, are formed by the termination 

 of its ribs. 



In the gramineous tribe, the leaves are smooth at the 

 margin, and have no indentures ; the ribs run on each side 

 along the margin like a small seam, and terminate at its 

 pointed extremity, whence all the exhalations take place. 



When the indentures of some leaves reach so far as 

 half-way down, they are said to be pinnatifid ; and when 

 the leaves, though separate, grow from one foot stalk, so 

 that one of them cannot fall off, or be separated from the 

 other without being torn asunder, the leaf is said to be 

 dissected. 



Caroline. There are a great variety of leaves of this 

 description : the rose, the acacia 



Mrs. B. No ; these are compound leaves,, and differ 

 from the dissected by being articulated, each leaflet hav- 

 ing a separate foot-stalk, which, when the leaf dies, de- 

 taches the leaflet from the general foot-stalk, and they fall 

 separately. 



At the base of the foot-stalk of compound leaves there 

 generally grows a small organ, called stipula: it consists 

 of two accessary leaves, as you see here in the rose-leaf, 

 the willow, and indeed in most exogenous plants. Some- 

 times the stipula is attached to the foot-stalk, at others to 

 the stem : it withers easily, and often falls off before the 

 other leaves ; for which reason it is not always to be met 

 with on branches of a certain age. In this branch of rose- 

 tree you see that there are stipula to all the younger shoots, 

 while the older ones have already lost them. In the pea 

 the stipula is larger than the common leaves. [See Plate 1.] 



289. How is the fifth one described and what ones does it include! 

 290. How are the indentures, or teeth of leaves formed'? 291. In 

 the gramineous tube, how are the leaves described! 292. When are 

 leaves said to be pinnatifid, and when dissected? 293. What is said 

 of the leaves of the rose, and the acacia! 294. What is the stipula, 

 and of what does it consist! 295. What is further said of the stipu- 

 la! 



