the Secretory Tissues of the Marattiaceae . 415 
As mentioned above, these elements generally arise just behind the 
generative tissues of the stem and root and are consequently subjected 
to a variety of stresses. The stretching of cells due to turgor increases 
as they pass from the embryonal condition and decreases as they assume 
their permanent condition, and since the mucilage-ducts in the stem or roots 
are generally surrounded by parenchymatous cells with thin walls of cellu¬ 
lose, it follows that the latter will tend to contract when the force of turgor 
is withdrawn. The negative tension thus called forth is considerable, and 
may account for the very rapid increase in the diameter of the mucilage- 
ducts which occur in the stem and roots of most of the genera and species 
examined (Figs. 8 and 13). 
The adult mucilage-ducts, which frequently branch and anastomose, 
pursue a very irregular course through the ground-tissue. 
The above description applies to the development of the mucilage- 
ducts in the following genera and species : 
Angiopteris evecta , Hoffm. (root excepted) (see also Methods ii and iii). 
Archangiopteris Henryi , Christ et Gies. (the material of this plant was 
unsuitable for determining this point with accuracy). 
Danaea alata , Sm. 
Danaea nodosa , Sm. 
Kaulfussia aescidifolia , Bl. (see also Method iii). 
Marattia alata , Sw. 
Marattia attenuata , Lab. 
Marattia Cooperi^ Mre. 
Marattia fraxinea, Sm. 
A slight variation from the usual type of development was sometimes 
observed in the roots of Marattia Cooperi. Here the mucilage-canals may 
originate from a single row of superposed cells with dense granular cyto¬ 
plasm. These initial cells do not divide, but rapidly undergo complete 
mucilaginous degeneration. The nuclei of these cells appear to be remark¬ 
ably resistant to the enzymes which cause the breaking down of the cells 
and their contents, and often retain their individuality for a very consider¬ 
able period after the complete collapse of the cells. They can frequently 
be found floating in the mucilage. 
In this case there can obviously be no doubt as to the true lysigenous 
origin of the mucilage-ducts (Fig. 10). 
Method ii. Protogenetic Schizo-lysigenous Mucilage-canals. 
In the petiole of Angiopteris evecta an alternative mode of development 
was noticed for many of the mucilage-ducts. These elements, to which both 
Brebner ( 2 ) and Lutz ( 14 ) had attributed a typical schizogenous develop¬ 
ment, were studied with special care. 
