Osborn. — Some Observations on Isoetes Drummondii , A.Br. 51 
four to five months when the plants are invisible below the ground, then at 
the end of May or in June following the spores are shed. 
The first stage in the process of spore dispersal is the separation of the 
sporophyll bases and sporangia from the subterranean stock and the forcing 
of them upwards through the soil to the surface. This is effected by the 
absorption of water in the walls of the mucilage tissue already described. 
The cell-walls of this tissue absorb water with great avidity, and as a result 
begin to swell (Fig. 13). Having the stock below them, and the soil 
around, the line of least resistance is towards the surface of the soil, so 
Fig. 12, a , b, and c. a, ripe sporangium wall in surface view, showing irregular arrangement 
of cells on flat upper surface and regular shape of cells of side-walls (at bottom of figure), b, cells 
in side-wall of ripe sporangium, c, transverse section of ripe sporangium wall, showing cells some- 
what distended with water and stout cuticle. Camera lucida outlines, x 93. 
that, expanding in this direction, they force the imbricate mass of sporo- 
phyll bases upwards until it reaches the surface (Fig. 3). 
The second stage depends upon the continued presence of an excess of 
moisture. Sooner or later the mass of sporophylls becomes sodden and falls 
apart (Figs. 14 a and 14 b). It is only now, when the walls of the sporangium 
are thoroughly saturated, that the liberation of the spores occurs. The 
thick-walled cells of the sporangium wall have absorbed moisture and tend 
to expand, but, being bounded externally by a cuticle which is less 
expansive than the cell-walls, the tension set up is such as to produce an 
eversion of the sporangium. First the wall ruptures at any point on its 
circumference. One or more segments of the tough wall tear away from 
