54 Osborn . — Some Observations on Isoetes Drummondii , A.Br. 
Summary. 
1. Isoetes Drummondii is a plant widely distributed in certain parts of 
South Australia, where it grows terrestrially in seasonal swamps during the 
period of winter rainfall. During the dry summer it aestivates, as do the 
other geophytes with which it is associated. 
2. The stock is buried to a depth of about i cm., and during the 
vegetative season only a small rosette of linear leaves is visible above 
the soil. 
3. The stock is trilobed, the projecting portion of each lobe being 
built up of a number of segments or caps, the caps being the whole of the 
leaf- and root-bearing portions of the stock developed in previous growing 
seasons. The abscission of such caps is a result of the regular alternation 
of growing and resting periods (during which there is great desiccation) in 
the life-history of a plant having the growth mechanism of an Isoetes. 
4. On the approach of the dry season the leaves dry up and become 
detached, leaving their tough bases and sporangia in situ upon the stock, 
wholly buried and invisible. 
5. Early in the rainy season following, the hardened bases of the 
sporophylls are forced above the surface of the soil in a projectile-like mass, 
carrying with them the sporangia, by the expansion of certain pads of 
mucilage cells formed at the close of the previous vegetative season on the 
extreme bases of the sporophylls and from the superficial cells of the 
leaf-bearing cortex. About the same time the leaves of the new vegetative 
season begin to appear. 
6. The imbricate mass of sporophyll bases breaks up upon the surface 
of the soil, and the spores are set free by a tearing away of the sporangium 
wall from its attachment to the sporophyll when sodden. This is due to 
a difference between the tension of the inner and outer surfaces of the 
sporangium wall when saturated, and results in an eversion of the wall. 
