Osborn. — Some Observations on Isoetes Drummondii , A.Br. 53 
point of interest that an examination of Isoetes Drummondii has brought 
out is that, as in other species of the genus, there is a regular annual 
production of sets of leaves and roots upon a special cortex developed to 
allow of their expansion. There is a close correlation between the growth 
of leaf- and root-bearing surfaces which finds its expression in the develop- 
ment of three lobes and three clefts in the leaf-bearing cortex, to correspond 
with the three grooves from which the roots appear. The climatic conditions 
under which Isoetes Drummondii grows, resulting in a regular alternation 
of vegetating and resting seasons, makes the annual production of roots and 
leaves unusually definite. 
Before a general discussion of the sporangial mechanism of the genus 
could be attempted much further information, derived from a study of 
various species in the field and with abundance of fresh material, is 
desirable. A further study of such species as /. Hystrix and /. Duriaei in 
the Mediterranean and of /. Buileri and other species growing in damp 
soil in the United States would be particularly interesting for comparative 
purposes. Whether any of these species would show a spore-dispersal 
mechanism comparable to that of /. Drummondii it is impossible to say. 
In this connexion it is interesting to recall the presence of cells with 
mucilaginous walls in the sporophyll of /. Hystrix } In this species the 
mucilage tissue is distributed in two strands lateral to the sporangia ; the 
function of these strands is at present uncertain. In whatever way the 
spores of /. Hystrix are freed, the mechanism of dispersal must be efficient. 
Durieu 1 2 describes ‘ un gazon fin et uniforme ’ covering certain hill-tops in 
Algiers, which he found to be composed of Isoetes , though at first the 
plants were mistaken for a grass. In South Australia it is easy to mistake 
the rosettes of /. Drummondii for those of some phanerogam. 
The vast majority of the Pteridophyta free their spores under dry 
conditions, the familiar mechanism of the annulus depending on progressive 
desiccation for its action. The liberation of the spores in the subaquatic 
species of Isoetes appears to depend upon a process of decay. In Isoetes 
Drummondii there is a special mechanism for freeing the spores which 
depends upon saturation with water, not on dryness, for its action . 3 Many 
of the other peculiar features of Isoetes Drummondii described above appear 
to be in the nature of preparations for this remarkable method of spore 
dispersal. 
1 Hill, T. G. : Ann. Bot., xx. 267-73, 1906. 
2 Quoted by Motelay, L., and Vendryes Reprint from Actes de la Soc. Linn, de Bordeaux, 
p. 95, 1884. 
3 As it stands, the case of Isoetes Drummondii would appear to be unique among the Pterido- 
phyta. Such xerophytic developments as the sporocarps of Marsilia and Pilularia afford only 
remote analogues. 
