54 
N. Bancroft. 
varieties which may or may not be quite distinct from the type. 
The form-cycles are those of Medullosa stellata, M. porosa, M. Solnisii 
and M. Leuckarti. A brief consideration of each one is necessary 
in view of the importance attached by various workers to the genus. 
In Medullosa stellata (Fig. 9) the peripheral steles or plate- 
rings are few in number and are much elongated tangentially so that 
Fig. 9. —Medullosa stellata v. typica. Transverse section of stem, showing 
pr, peripheral vascular system ; and sr, star-rings of the medullary system. 
(Adapted from Weber and Sterzel, 1896). 
they collectively form an almost continuous ring with few inter¬ 
ruptions. There are numerous star-rings, mostly large in size. The 
varieties of the type depend mainly upon the degree of continuity 
of the outer stelar system and on the variations in thickness of the 
wood on the inner and outer sides of this system; variety gigantea, 
however, presents an additional complication in the development of 
