1922] BENSON—HETEROTHECA GRIEVII 129 
regarded as determined. The peripheral strands probably alter- 
nated with every two series of loculi, but owing to the obliquity 
of their course (fig. 10 and text-fig. 7) they are often difficult to 
distinguish. An interesting point in the structure of the sporange 
in detail is the absence of any evidence of the building up of the 
synangium by a fusion of sporangia. The whole body strongly 
suggests its origin from a single sporange which has shared in the 
same type of skeletal elements as the petiole on which it was borne. 
The sporogenous regions were distributed fairly equally through- 
out the body, except that their disposition in the periphery prob- 
ably was determined by the approximately dictyoxylon type of 
cortex. If the loculi appear to be of unequal size, this is due 
partly to the varying girth of the sporange, and partly to the plane 
of section through the loculus. Wherever a section occurs in the 
surface plane, as in the upper third of text fig. 3, the buttresses 
are seen to lie so obliquely that a transverse section necessarily 
cuts through the contained loculi at different angles, and explains 
the fact that a transverse section does not differ much in appear- 
ance from a longitudinal one, except in form. 
GROUPING OF SPECIMENS.—The available specimens, roughly 
sixty in number, may be grouped in four classes: 
Crass I.—Specimens such as that occurring in CN .307.16-19 
(figs. rr and 12), where the vegetative tissue is subordinate in 
amount to the sporogenous tissue. Such specimens show septa, 
mesarch vascular strands, and only a few water storage elements. 
The sclerotic plates characteristic of Heterangium in such sporangia 
are well developed, both in the periphery and in connection with 
the deeper lying septa. 
Crass II.—Specimens such as those occurring in CN.411.30, 31 
and CN .386.17, 18 (figs. 5, 10). These contain ripe, apparently 
normal spores and normally disposed loculi, but undoubtedly a 
larger proportion of vegetative tissue than those in class I (text 
figs. 3, 4). The following series also belong to this class: CN. 
386.7, 8; CN .395.5, 6, 18, 19; CN .396.4, 5. 
Crass III.—Specimens such as those occurring in CN .383. 
to-13 and CN .386.11, 12 (figs. 1-4, 8, 9). Although one of these 
is possibly an immature form showing carbonization of the spo- 
