444 Kashyap . — Notes on Equisetum debile , Roxb. 
millimetre in length and considerably less in width. They bore archegonia 
or antheridia. The occurrence of antheridia alone on the prothallia is 
interesting, as they are never found alone in the prothallia, growing at a 
distance from each other in the laboratory or in the wild state. In the latter 
state the prothallia are always scattered, clusters never having been observed. 
In the scattered prothallia archegonia are always formed first and antheridia 
arise only on the older prothallia. The prothallia arising in clusters from 
thickly sown spores are thus extraordinarily similar to those of other 
species of Equisetum figured by Buchtien and others. The lobes, however, 
in the prothallia of Equisetum debile are always erect in whatever condition 
the prothallia may be growing, thus differing from the lobes of those of 
other species which are spreading. It is possible that in some cases at least 
the prothallia of other species of Equisetum remain small owing to the 
spores having been sown thickly. It would be interesting to find out the 
behaviour of the spores of some other species of Equisetum when sown 
far apart. 
It may also be mentioned that though in nature the prothallia do not 
last more than a few months, dying before the end of April, it is possible to 
keep them growing for a longer time, and perhaps for some years. The 
stoppage of growth and ultimate death is apparently due to two causes — 
the formation of the embryo and the heat of the summer. During 1915-16 
some prothallia were kept in a glass-house from September 1915 to July 
1916. The embryos as they were developed were cut away and the pro- 
thallia were protected from the heat in the glass-house. Thus they had 
been living for three months more than their ordinary life when unfor- 
tunately all the flower-pots containing them were submerged under water 
during a heavy downpour of rain and the prothallia were all killed. During 
the last two months of their existence the growth was very slow and parts 
of the prothallia died, leaving separate lobes growing independently. They 
would have very likely resumed their active growth in September again if 
they had lived up to that time. 
Summary. 
1. The endodermis . The endodermis in Equisetum debile is very 
unstable. At the nodes of the underground and aerial sterile shoot and in 
the fertile region the endodermis surrounds each vascular bundles separately. 
In the internodes of the underground and aerial sterile shoots there is 
a transition from the separate endodermis round each bundle to two endo- 
dermal layers, one external and the other internal, round the ring of 
bundles as a whole. This transition is independent of the distance from 
the node of that part of the internode where it occurs. The two rings of 
endodermis fuse here and there, leaving islands of parenchymatous tissue in 
the interfascicular region. At the point of junction of the two layers a 
