BICOLLATERAL BUNDLES 8i 



and outer (Fig. 37). Two groups of phloem occur in each bundle, 

 one external (Ph.'), separated from the xylem b\- the cambium 

 (Ca), the other internal (Ph."), separated from the protoxylem 

 (P.xy.) by ordinary parenchyma. Such bundles, termed bicol- 

 lateral, are not uncommon in certain families of Flowering Plants, 



Fig. 37. — Diagram of a transverse section of the stem of tlie Vegetable 

 Marrow {Cucurbila), Ca,, cambium ; Col., coUencliyma ; Ep., epi- 

 dermis ; jl/..r_y., metaxj'lera ; PA.', outer phloem ; PA.", inner phloem ; 

 P.xy., protoxylem ; Scl., sclerenchyma (black). 



such as the Cucumber -family or Cucurbitaceae (to which the 

 Marrow belongs), and the Potato-family or Solanacefe, and offer 

 a marked contrast to the normal collateral type seen in the Sun- 

 flower. The elements of both xylem and phloem are remarkably 

 large, and are therefore especially suited for a study of their 

 detailed structure, which can be rendered more distinct by 

 staining with eosin (see Appendix VI). 

 6 



