302 



Holm — Studies in the Cyperacece. 



cells, while the lower epidermis consists of somewhat smaller 

 cells. The mesophyll is in this part of the involucre composed 

 of rather long, loosely connected cells, all destitute of chloro- 

 phyll, giving the leaf the peculiar white aspect in contrast to 

 the upper part, in which the mesophyll is of usual structure 

 and well provided with chlorophyll. The mestome-bundles 

 are small, but represent, nevertheless, the same forms as we 

 have described as characteristic of the proper leaves ; cells 

 containing tanniu were observed in the mesophyll and in the 

 hadrome. Stomata were observed, but confined to the lower 

 surface of the green part of the involucre. 



As to the aerial stem : this is perfectly smooth, terete, 

 slightly furrowed and hollow. It contains a bark rich in chlo- 

 rophyll and composed of about eight layers of very regularly 

 arranged palisade-cells, which are closely packed, except 

 underneath the stomata, which are well represented in the epi- 

 dermis. The palisade-tissue does not form closed rings in the 



x... 



Fig. 3. Transverse section of the stem of D. leucocephala. Ep, Epidermis ; 

 S, Stereome ; Fj vessels; F ) fundamental tissue. 320 x natural size. 



stem, but is interrupted by the stereome which support the 

 mestome-bundles. There are three concentric bands of mes- 

 tome-bundles in the stem, and they are very regularly arranged 

 and represent three degrees of development. Those of the 

 outer- and inner-most band show exactly the same development 

 in regard to the mestome ; the leptome and hadrome are very 



