Danaea and other Marattiaceae . 541 
they have been shown to be of real use in aiding specific dis- 
tinction in certain cases. The crystals and mineral deposits 
of the Marattiaceae have been studied by several observers, 
e.g. in more recent times Montverde, Kuhn, and Radlkofer. 
The structure of the meristeles, although distinctive of the 
group, does not afford means of generic or specific distinc- 
tion. Taking the Marattiaceae collectively it may be said 
that they do not possess many diagnostically valuable histo- 
logical characters. 
The petiole and rachis are generally somewhat flattened 
on the upper surface. In the rachides, especially of the 
second and third order, there are projections from the angles, 
and there is a median ridge which becomes more prominent 
towards the apices. In some species the lateral ridges become 
wing-like, hence the specific term alata . These are specially 
mentioned because they are the only parts of the axes which 
have numerous rodlets projecting into the intercellular spaces 
from the walls of the cells. The rodlets however occur 
abundantly in the mesophyll of the lamina. It looks just 
as if there had been a viscid mass between the cell-walls, 
so that when the intercellular spaces were formed, it was 
drawn out into stringy masses, the threads of which parted 
in the middle as the walls receded from each other. Accord- 
ing to Mangin 1 these rodlets consist of pectates, chiefly 
calcium pectate. Whereas these rodlets are very well marked 
in Angiopteris , Marattia , and Kaidfussia, they are almost, 
if not quite, absent in Danaea simplicifolia and elliptica , 
although present in other species. 
In none of the genera do the meristeles of the leaf differ 
essentially from those of the stem. The chief difference is 
in the position of the protoxylem, which is normally endarch 
in the frond, endarch and mesarch in the dictyomeristeles 2 . 
In a few cases two or three xylem-elements (PI. XXIII, 
Fig. 22, mx /) were found to the inside of the protoxylem, 
1 Mangin, Etude historique et critique sur la presence des composes pectiques 
dans les tissus des veg^taux, Journ. de Bot., v. 1891, vi. 1892. 
2 Shove, loc. cit., p. 5 1 3. 
