66 PRACTICAL BOTANY. 



2. Procambium, which is the formative tissue of 

 the vascular bundles. Trace its continuity with these. 

 Between the procambial bands and the dermatogen 

 lies 



3. The formative tissue of the Cortex, which is 

 (partially at least) characterised by dark-looking 

 intercellular spaces. 



4. Centrally lies a dark bulky cylinder, which is 

 continuous with, and formative of, the Pith. 



Observe carefully the mode of origin of the leaves. 

 They appear at the periphery of the cone as protuber- 

 ances of the dermatogen and the subjacent cells. 

 As they increase in size their internal tissues become 

 differentiated into (1) procambium, which is subse- 

 quently connected with that of the stem, and (2) tissue 

 with intercellular spaces, which is continuous with the 

 cortex. At the same time single cells of the dermatogen 

 grow out, and divide, so as to form the conical multi- 

 cellular hairs, which cover the surfaces of the leaves 

 (cf. leaf-section). In the older leaves of the bud the 

 development of the emergences around and below the 

 bases of these hairs may be traced. 



Note on passing back from the apex towards the 

 more differentiated part of the stem a gradual increase 

 in length of the cells, corresponding to the gradual 

 extension of the internodes, while in the stem 

 (internode) below the bud this is very marked. Ob- 

 serve also the various stages of the process of vacuoli- 

 sation of the protoplasm. 



In cases where the apical cone is broad, as in Helianthus, the 

 tissues, with the exception of the dermatogen, are usually not 

 sharply denned from one another at a point immediately below 



