Danaea and other Marattiaceae . 547 
inwards, or centripetal (cf. Fig. 26). Moreover, it is difficult to 
understand what is meant by the statement that the tracheae 
are simultaneously developed in a quadri-radiate manner in the 
centre, and that subsequently smaller thick-walled tracheae 
are added partly in secondary rays 1 . There can be no 
question of a constantly quadri-radiate central differentiation, 
because all types of root from the diarch to the polyarch are 
formed in the course of the development of the seedling to 
the full-grown plant. The writer observed nothing in the 
many roots examined, both young and old, which suggested 
anything different from the normal development of a root 
central-cylinder, or actinostele. 
Mucilage Canals. 
The lysigenous view of the development of these structures 
has again found strong support, for Farmer and Hill 2 throw 
in the weight of their opinion in its favour. 
The writer advocated the schizogenous view as a result of 
his examination of the development of those structures in the 
root and frond of species of Marattia and root of Danaea 
simplicifolia. A careful re-examination of the preparations 
originally made seems to the writer to still justify his belief 
in the schizogenous origin of these structures, but the sections 
were hand-cut, and there is always the risk that something 
may have dropped out. On the other hand, microtome- 
series made from material imbedded in paraffin and cut by 
the ‘ rocker J are not quite satisfactory, because the sudden 
impact on the knife-edge breaks the epithelial walls, and 
frequently displaces the cell-contents. It seems to the writer 
that the only means of satisfactorily settling this question is 
to imbed in celloidin and cut with a sliding microtome. 
Review of Terminology in relation 
to Morphology. 
As indicated in the introduction on terminology, certain of 
1 ‘Die primaren Gefasse werden in Form eines Vierstrahlers im Centrum 
gleichzeitig angelegt, spater schliessen sich daran dickwandigere, kleinere Gefasse, 
teilweise in secundaren Strahlen.’ 2 Loc. cit., p. 390. 
P p 
