218 SIR JOHN LUBBOCK ON 
teeth. The stipules form a very efficient protection to the leaves 
till they attain considerable size. 
In Lathyrus latifolius,Linn., the upper limb of the stipule also 
protects the younger leaves, which, however, have only one pair of 
leaflets, and do not therefore occupy so much room. The stalk, 
however, being very wide is not covered by the sheathing-stipule. 
Consequently, if the upper one had a lower limb on the outer 
side, it would be exposed. The single limb, which is on the inner 
side, lies snugly ensconced between the stem and the older leaf. 
It is not therefore in the same plane as the upper limb. More- 
over, the function of the stipule being to protect the young bud, 
it develops early, and where it is full-grown the lower limb 
(fig. 24) is equal in length to the internode below. Subsequently, 
however, the internode becomes mueh longer, while the stipule 
remains as before. But though the stipule may be correctly 
described as half-sagittate, it shows a minute tooth where the 
other barb would have been, indicating that it is descended from 
ancestors which had a barb on each side. 
Tn L. pratensis, Linn., the stipules (figs. 19, 21, 22) are sagittate. 
Figs. 21, 22, 23, 24. 
Lathyrus pratensis. Lathyrus latifolius. 
