154 Boeshore — The Morphological Continuity of 



In G. aphylla (Plate XIV, Fig. 10) a very marked condensa- 

 tion occurs. The stem is slender, rather wiry, unbranched, 

 and from 6 to 18 inches in length. The leaves, much reduced in 

 size, are scale-like, tapering almost to a point, and closely ap- 

 plied to the stem. Stomata are distributed over the leaf surface 

 in comparatively small numbers when the entire foliage of the 

 plant is taken into account. Leaves and stem are covered with 

 short, conical, unicellular hairs. 



Transverse sections of the stem taken at the same level as 

 in the preceding genera are smaller in circumference. Stems 

 tend to become quadrangular, being reinforced by scleroid cells 

 at the angles. A rather wide green cortex surrounds the bundle 

 system. Phloem consists of about equal amounts of hard and 

 soft bast. Xylem is well developed and wide, enclosing a small 

 pith area. 



G. aspera (Plate XIV, Fig. n) shows further reduction in 

 height of stem. The internal structure is very similar to that of 

 G. aphylla. Stem and leaves have hairs similar to those of G. 

 purpurea. 



Condensation advances even more markedly in Harveya and 

 Hyobanche (Plate XIV, Fig. 12, 13) in that the stem is only from 

 4 to 6 inches in height. Both genera are parasitic, have scale-like 

 leaves or these even reduced to functionless scales. Wettstein 

 (22,p.97) describes Hyobanche as a fleshy low, parasitic plant with 

 numerous scale-formed leaves, the lower scales being smaller 

 than the upper ones. Material of this genus was not available 

 for study, but the foregoing description regarding the fleshy na- 

 ture of the plant suggests a very strong tendency toward genera 

 of Orobanchaceae. 



Transverse sections of the stem of H. coccinea have a wide 

 pith around which the ring of bundles is arranged. These are 

 more simplified than in the preceding genera, and in this respect 

 Harveya is a good transition from species of Gerardia to Oroban- 

 che of the Orobanchaceae, in fact it is closer to Orobanche than to 

 Gerardia. The xylem, while forming a continuous ring, is nar- 

 row in places and irregular; its elements are spiral tracheae and 

 pitted vessels. The phloem is in excess of the xylem, soft bast 

 of 1 to 3 layers of cells in patches, and hard bast that is very strik- 

 ingly developed as 3 to 6 layers of cells forming a solid ring about 

 the soft bast. The cortex is as wide as the phloem and xylem 



