366 



MANUAL OF BOTANY 



frequently they form also independent circles in the cortex or 

 the pith. 



The secondary bundles formed by the cambium have no 

 connection with the leaves ; they are cauline bundles only. 



The branches of the stem arise, as we have seen, in the axils 

 of the leaves by development there of lateral growing points 



Fia- 749. 



Fig. 749. Aquatic stem of Marsilea. ep. Epidermis, co.la. Cortical 

 lacuiiEE. scl. Sclerenchyma in the cortex, en^. Outer ; en^. inner fused 

 endodermis of the steles. The steles are fused together laterally, forming 

 a vascular ring in the centre of the stem surrounding a small portion of 

 the ground tissue. 



which arise as small protuberances on the side of the main one 

 (fig. 747). They arise only from the periblem and the epidermal 

 layer, as do the leaves in whose axils they occur. As they 

 develop, their structure is found to be similar to that of their 

 parent ; they show the same merismatic layers, each of which 

 becomes continuous with the corresponding layer of the latter. 



