440 Kashyap. — Notes on Equisetum debile , Roxb. 
endodermis of the second type, and an endodermis of the second type is 
associated with one of the third type. Since underground organs, e. g. the 
root of vascular plants, retain their ancestral structure for long periods and 
through many phyla, it appears that an endodermis of the second and the 
third type has been gradually derived from that of the first type. This 
view is borne out by the writer’s observations on the endodermis of E . debile. 
E. debile is the most variable species of the whole genus as regards the form 
of the endodermis in the stem. In a very general way it may be stated that 
in the internode of the underground rhizome the endodermis belongs to the 
first type ; in the aerial vegetative shoot it is of the first type near the node 
but of the second type in the internode ; and lastly in the fertile shoot 
below the cone as well as in the cone, so far as it can be traced upwards, it is 
of the first type. At the same time, in the internodes of the underground 
as well as the aerial portions, the two types, first and second, merge into 
each other. The transition is met with at all places in the internode 
irrespective of its nearness to the node. In those species where two layers 
of the endodermis occur, one external and the other internal to the ring of 
the vascular bundles, the band of parenchyma lying between the two layers 
in the interfascicular region is usually very narrow owing to the external 
endodermis being bent inwards in that region. In Equisetum debile these 
two layers are actually fused in certain places so that a complete closed ring 
of endodermis is formed, not only round one or more bundles, but isolated 
rings of endodermis are also pinched off in the interfascicular region, pro 
