Development of Cassytha filiformis, L. 409 



lar. The cells also contain chloroplasts and considerable 

 protoplasm with large round nuclei and nucleoli. Internal 

 to this is a zone of hard bast (3), broken by rays of large 

 cortical cells into smaller and larger patches, rather irregu- 

 lar in arrangement. The bast cells are somewhat larger 

 than the phloem cells, but smaller than cortical cells and the 

 lumen is reduced to a minimum. Beneath each patch of 

 hard bast is an irregular space, formed by the degeneration 

 of phloem, of which the flattened remains usually appear on 

 the inner border of the space (Fig. 4), but which seem on 

 the whole very feeble and unimportant. The rays separat- 

 ing these patches contrast somewhat with the outer cortical 

 cells, with which they are continuous, in their larger size 

 and comparative emptiness. 



The wood is arranged in a continuous ring beneath the 

 phloem patches. In the old stem medullary rays are faintly 

 recognizable. The wood elements grow larger toward the 

 centre of tlie stem, and the most internal elements are very 

 large pitted vessels, eight to ten in number (5). 



Extending far into the pith are five to seven patches of 

 delicate internal phloem cells (8), each patch enclosing three 

 or four thickened cells of protoxylem (7), in rows or 

 separate. The pith consists of large cells with intercellular 

 spaces and without starch or protoplasmic contents. They 

 have very thin walls and look quite empty. 



A study of the parts of the mature stem in detail shows 

 the epidermis to be provided with copious stomata, placed 

 transversely on the stem, and arranged in longitudinal rows, 

 which are slightly depressed below the surface, as has been 

 already noted by Hackenberg * and other authors. As 

 the stomata lie transversely, the cross section presents the 

 appearance given by longitudinal sections of ordinary plants, 

 and the usual appearance of two adjoining guard cells must 

 be sought in the longitudinal section. The stomata are in 



* Verhandl. d. naturhist. Vereins d. Rhein. u. Westfalen, V. 6, 

 Bonn, 1889. 



