Danaea and other Marattiaceae . 
543 
oblique end-walls, the number of plates varying with the 
obliquity of the wall. Besides these plates, isolated pits 
( ponctuations) , or small groups of them, occur on the longi- 
tudinal walls. The contents of these sieve- tubes is a highly 
refringent liquid containing a number of refringent sphaerules 
in suspension, which are specially aggregated in the region 
of the pits. The wall consists of cellulose. The sieve-plates 
and pitted areas are actually perforated. No callus occurs. 
The exceptional position of the protophloem in this group 
of Ferns is very remarkable, and it is matter for wonder and 
speculation why the Marattiaceae alone, so far as is known, 
possess it. A reason for its position can readily enough be 
found, viz. the more ready conduction of nitrogenous food- 
material to the developing xylem on the one hand, and the 
later formed phloem on the other. Once the advantage 
of such an arrangement is realized, the puzzle is not why 
should the Marattiaceae show this peculiarity, but why do 
not many other Pteridophyta and Spermophyta show it like- 
wise ? The internal phloem is developed a good deal later, 
and it has no protophloem, the protophloem only occurring 
on the outer face of the xylem and occasionally only just 
turning the corner at the ends of the xylem-plate \ 
In the Marattiaceae, as in other cases among Ferns, the 
concentric type of meristele which is characteristic of the 
frond generally, becomes collateral in the finer veins. In this 
there is a return to the condition found in the seedling, in 
which, at any rate in Danaea simplici folia, the first veins have 
no phloem on the inner or upper side. Fig. 23 illustrates one 
of the lateral veins of a fair-sized frond of Danaea simplicifolia , 
near its base. The meaning of the xylem being broken up 
into three parts could not be ascertained. It was thought 
that it might be associated with the dichotomy of the veins, 
but the same arrangement occurs above as well as below the 
fork. Fig. 24 shows still further reduction of the phloem, and 
at the same time another case of endarch protoxylem. The 
section was made from a fine vein of Marattia cicutaefolia. 
1 Cf. Shove, loc. cit, p. 513, par. 3. 
