SUNFLOWER. STEM. 65 



in glycerine : examine with low power, and then 

 observe 



1. That the axis ends in a naked, broadly-conical 

 Apex (punctum vegetationis), which is surrounded and 

 enveloped by 



2. Leaves : these may be observed in various stages 

 of development, the youngest being nearest to the 

 apex (i.e. their order of development is thus acropetal) ; 

 the surfaces of the older leaves are covered with 



3. Hairs, which are absent from the apical cone 

 and the youngest leaves (i.e. the hairs are developed 

 subsequently to the leaves themselves). 



Note (with a higher power) that the apical cone itself 

 consists of thin-walled cells with plentiful protoplasm, 

 which are smaller than the cells of the mature tissues 

 already studied, and are in a state of active division (i.e. 

 are meristematic). The whole meristematic mass is 

 differentiated into parts, which maybe distinguished more 

 or less clearly from one another, and their continuity 

 may be traced with the several tissue-systems of the stem 

 and leaves, of which in fact they are the formative 

 layers. We may thus distinguish the following : 



1. The Derm ato gen, as a single continuous layer 

 of cells, which divide only in a direction perpendicular 

 to the external surface of the organ (stem or leaf), 

 which it covers completely : it is easily seen to be 

 continuous with the epidermis, of which it is the 

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

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

 permeated by intercellular spaces filled with air. It is 

 traversed at a short distance from the external surface 

 by transparent, longitudinal bands of 



F 



