Igtt] CHARLES—ANATOMY OF MARATTIA gI 
branches less and less frequently, until it finally joins the main 
vascular system and is not given off again (fig. 25). At the 
same time the strands of the main vascular system unite into a 
solenostele with a single leaf gap. This is the same sort of behavior 
as that in the plant examined by METTENTUS (21). The compact 
habit of Marattia is therefore responsible for two of its most strik- 
ing differences from the Psaroniae (22): the shape of the bundles, 
which are band-shaped in Psaronius and elliptical in Marattia; 
and the relation of the medullary system to the leaf traces. 
The relation of the roots to 
' the external and to the medul- 
lary systems differs in the 
mature stem examined by Miss 
SHOVE (26) and in the young 
stems of Maraitia. In the 
latter the main root supply 
joins the external system, while 
the medullary system has a 
few small roots. In Angiop- 
teris the largest number of 
roots is attached to the internal 
system. This difference may be Fic. 2c.—Upper end view of fig. 2a. 
due to the greater importance 
of the internal system in the older stem, or to the possibility that 
the meshes that apparently belong to the external system in the 
mature stem really belong to the leaf traces, and the second zone 
is homologous with the main vascular system to the young stem. 
In comparing the medullary systems of Marattia and the so- 
lenostelic ferns’ described by GWYNNE-VAUGHAN, some important 
differences appear. In the latter the origin of the system is the 
elaboration of a thickened leaf gap margin. The thickening works 
upward and downward, and in Alsophila (11) the strands are decur- 
rent into the pith. In Marattia alata the origin is from an internal 
branch above a leaf gap, from the top of a leaf gap, or from a 
cambium in the medulla. In the solenostelic ferns the connections 
of the medullary with the main vascular system are generally at 
the nodes and along the leaf gap margin, although in Pteris elata 
