112 PRACTICAL BOTANY 



1. The axis, which is wide below, but tapers upwards to 

 the rather elongated apical cone (punctum vegetationis). 

 The axis is composed of the several tissues already no- 

 ticed. Note especially in the lower part of the section 



a. The rectangular intercellular spaces, divided 

 transversely by diaphragms at the nodes. 



b. The axile vascular cylinder, which may be 

 followed far up into the apical cone, and which gives 

 out lateral branches to the leaves. 



2. The leaves, diminishing in size towards the apex. 

 Note the scale-hairs about the bases of the leaves. 



Put on a high power, and examine the apical cone. 

 Note 



1. The dermatogen, a continuous layer of cells, 

 which covers the apical cone externally. Trace it back- 

 wards from the apex : it will be seen to give rise to the 

 epidermis. 



2. The periblem, consisting of 4-5 layers of cells, 

 Avhich may be traced backwards, and be thus shown to 

 give rise to the cortex. 



3. A central cylinder of plerome, which is continu- 

 ous with, and gives rise to, the vascular cylinder 

 (compare the diagram, Fig. 5, p. 80). 



Note that the leaves originate from the outgrowth 

 of the dermatogen and periblem, the plerome taking no 

 part in their formation. Also that the vascular system 

 of the stem is already developed at a higher point on 

 the axis than that of any of the leaves. We have thus 

 an instance of cauline vascular bundles, that is such 

 as are proper to the stem, as distinguished from com- 

 mon vascular bundles, which terminate at their upper 

 extremities in the leaves. 



