THE DIFFEEENTIATION OF THE PLANT-BODY 27 



the three regions already alluded to. The stem of Equise- 

 tum and the leaves of Conifers are furnished with a layer 

 of thick-walled cells immediately under the epidermis 

 (fig. 30) ; the vascular bundles of many Monocotyledons 

 are surrounded separately by a sheath of small cells of 

 similar character (fig. 31) ; in Pennisetum a sheath is 

 developed round the stem in the form of a hollow cylinder 

 which lies between the bundles and the epidermis. 



More frequent instances occur in which two of the 



FIG. 30. LEAF OF Pinus (ONE OF THE CONIFERS). 



ep, epidermis ; hy, layer of sclerenchyma ; et), endodermis ; v.b., vascular 

 bundle ; r.d., resin duct. 



regions in question are strengthened simultaneously. In 

 the stems of Scirpus there is a development of sclerenchyma 

 round the periphery, and strands occur also in connection 

 with the bundles. Sometimes these are connected by 

 bands of sclerenchyma lying between them. In Fimbri- 

 stylis there is a ring of sclerenchyma in the cortex and 

 patches around the periphery, which in other cases are 

 joined like those of the former type. In the stems of 

 Typha a band of sclerenchyma lies at the back of each 

 bundle, and either a ring or some isolated strands may be 



