ON LEAVES. 65 



They commonly shoot at the articulation of a leaf, be- 

 cause the branching off of the vessels offers some little im- 

 pediment to the flowing of the sap ; a small portion of it 

 is arrested in its course, and forms a deposition of food, 

 which a neighboring germ quickly applies to its own use, 

 and is thus ushered into life. 



Emily. Such germs must exist then in a latent state 

 in every part of the stem, and wait only for means of 

 sustenance to make their appearance externally. 



Mrs. B. In all probability ; for wherever there is an 

 accumulation of sap, a germ is sure to be developed. 



Emily. When I plant a slip of geranium, I take care 

 that it should have at least one leaf; because I know by 

 experience, though I was quite ignorant of the cause, 

 that the shoot would spring from the articulation of the 

 leaf. 



Mrs. B. In geraniums there is also another species 

 of articulation, consisting of knots in the stem, which an- 

 swers the same purpose, by interrupting in some meas- 

 ure the circulation of the juices, and affording a little sup- 

 ply of stagnant sap. Pinks and carnations, reeds and 

 rushes, the stems of corn and grass, are all intersected in 

 a similar manner. 



Caroline. Then when carnations and pinks are prop- 

 agated by layers, the shoots take place at those inter- 

 sections of the stem. 



Emily. Excepting the geranium, the leaves of all these 

 plants are, I believe, sessile ; the intersections in the 

 stems, must therefore supply the place of articulations in 

 furnishing the buds with food. 



Mrs. B. Precisely so. They belong to the class of 

 endogenous plants, whose leaves are more rarely articu- 

 lated than those which are exogenous. These intersec- 

 tions, however, not unfrequently occur in the latter, as 

 with the geranium, the vine, and several other dicotyle- 

 dons. 



345. Why do they shoot at the articulation of a leaf? 346. What 

 is said by Emily of such germs existing in a latent state 1 ? 347. When 

 planting a slip of geranium why has she been careful to have at least one 

 leaf? 348. In what besides geraniums is there another species of ar- 

 ticulation, consisting of knots in the steml 349. Of what description 

 are the leaves of all these plants, excepting the geranium'? 350. To 

 what class of plants do they belong'? 



