SUNFLOWER APICAL BUD 49 



it is the formative layer. Within this is a solid mass of tissue, 

 which looks for the most part dark, owing to its being per- 

 meated by intercellular spaces filled with air. It is traversed 

 at a short distance from the external surface by transparent, 

 longitudinal bands of 



2. Pro cambium, 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 (periblem) which is 

 (partially at least) characterized 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 protuberances of the 

 dermatogen and of the subjacent cells : the divisions in the 

 dermatogen are all anticlinal, those in the lower layer are both 

 periclinal and anticlinal. (Compare Fig. 4.) As they increase 

 in size their internal tissues become differentiated into (i) 

 procambium, which is subsequently 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 

 multicellular hairs, which cover the surfaces of the leaves. In 

 the older leaves of the bud the development of the emergences 

 around and below the bases of these hairs may be traced : 

 these are not represented in the diagram (Fig. 4). 



Note on passing back from the apex towards the more dif- 

 ferentiated part of the stem a gradual increase in length of the 

 cells, corresponding to the gradual extension of the internodes, 

 while in the first elongated internode of the stem below the 

 bud this is very marked. Observe also the various stages of 

 the process of vacuolization of the protoplasm ; this will be 

 best seen in sections stained with haematoxylin, and mounted 

 in Canada balsam. 



Apical buds of the Jerusalem Artichoke (Helianthus tuberosus) 

 may be used instead of H. annuus, and they have the advantage 

 of being vegetative buds. Whereas the Sunflower flowers 



E 



