Danaea and other Marattiaceae . 
549 
be used at the present time ; in fact, ‘ mondesmic ’ has already 
been used by Scott in his ‘ Studies in Fossil Botany 5 1 in the 
sense of possessing one strand. It would unnecessarily 
expand this paper to discuss the various additions to 
botanical knowledge which are bringing about this change 
of attitude. Perhaps the time is hardly yet ripe, but the day 
does not now seem far off when the three histogenetic layers, 
as well as cortex, pith, endodermis, pericycle, &c., will have 
lost to a great extent their present morphological connotation 
and be used simply as convenient descriptive terms in certain 
cases. 
Resume and Conclusions. 
Development of the Vascular System of Danaea. The 
vascular system is developed from a simple type of stele, a 
haplostele. The haplostele does not pass through a medul- 
lated stage, but becomes crescentic after the successive 
departure of a variable number of leaf-traces. When this 
stage is reached the next leaf-trace passes off from the con- 
vexity of the crescent, thus causing a distinct leaf-gap. Two 
meristeles are left behind with what is usually considered 
extrastelar tissue between them. The crescent gap is closed, 
a leaf-trace is given off, the gap again closed, &c. By the 
repetition of this process, followed by branching, anastomosis, 
and increase in number of leaf-trace meristeles, at length a net- 
work of strands or the dictyostele is formed. At one level or 
another a transitory solenostelic stage intervenes owing to the 
closure of one leaf-gap before the next one is opened. Also at 
no very definite level a strand arises as a branch from the con- 
cavity of the crescent, pursues an upward spiral course anas- 
tomozing with the large gamomeristele formed to close the 
successive leaf-gaps, so to speak, and at the same time give 
rise to the root. This central commissural column, or central 
strand, later gives off two branches which however reunite on 
their upward course. In this way then the irregular stelar 
network of Danaea simplicifolia is built up, and is shortly 
expressed by the statement that it is an adelosiphonic dictyo- 
1 l. c., p. 303. 
P p 2 
