the Secretory Tissues of the Marattiaceae. 41 7 
These ducts appear subsequently in old mature tissues and are therefore 
hysterogenetic. 1 
In the young petiole of Kaulfussia numerous mucilage-ducts, which 
develop according to Method i, occur, whilst in the young roots of Angio- 
pteris evecta no mucilage-ducts were observed. 
This may explain why Van Tieghem ( 20 ) failed to find mucilage- 
ducts in the roots of this genus. But numerous mucilage-ducts in all 
stages of development were observed in sections through fairly old petioles 
of Kaulfussia aesculifolia and through adult roots of Angiopteris evecta . 
These elements were found in perfectly healthy petioles and roots, and the 
hypothesis that these canals are formed as the result of traumatic stimuli 
was proved to be untenable. 
They arise by the collapse of groups of typical parenchymatous cells 
which are in other respects indistinguishable from the other cells which 
constitute the cortex. 
At an early stage these cells can be distinguished by a decrease 
of turgidity which results in a slight decrease in size, whereby the inter¬ 
cellular spaces, which are typically rather large between the cells of the 
cortical parenchyma, exhibit a corresponding increase in size. But no 
signs of mucilage were observed in these intercellular spaces. 
Meanwhile the cell-walls rapidly dissolve, while the cell contents become 
mucilaginous. The cells ultimately break down, and their disorganized, 
remains coalesce to form the stringy mucilaginous contents of the cavity 
(Figs. 7 and 9). 
As Newcombe ( 1 . c.) pointed out, when lysigenous cavities arise subse¬ 
quently to primary growth, there is generally a collapse but little or no 
tearing of cells. 
The development of these peculiar mucilage-ducts seems to be very 
irregular both in time and space. The fully developed ducts often exhibit 
a striking appearance, for they may be very irregular in outline and 
occasionally attain large dimensions, as is shown in Fig. 9. 
2. Development and Structure of the Tannin-sacs and Tannin-ducts . 
Cells containing tannin are widely distributed throughout the sporo- 
phytic tissues of all six genera of the Marattiaceae. 2 
They are generally protogenetic and occur either singly or associated 
together in groups. When they occur singly they can easily be distinguished 
by their tanniniferous contents from the neighbouring cells, from which they 
may or may not differ in shape or size. 
Their form varies in different regions of the same organ, but as 
1 Frank, 1 . c. 
2 The present writer’s observations on Kaulfussia cannot be reconciled with the statement of 
Campbell ( 1 . c., p. 185) that in this genus ‘tannin-cells are practically entirely absent from the 
sporophyte throughout its whole existence 
