320 Williamson. — Anomalous Cells within Tis sties 
in the two macrospores, Figs. 15 and 16, though I am far from 
concluding that all these various examples of contained cells 
are homologous. 
The question remains, what are these intrusive cells ? So 
far as Figs. 11, 12, 13 and 14 are concerned, I think we shall 
not risk making any great mistake in concluding that we 
have in them genuine examples of the so-called thylosis. 
The structures so named vary in different examples, but it 
appears to me that the specimens now described approximate 
sufficiently closely to the general type of thylosis to be 
legitimately recognised as examples of it. But it is other- 
wise with the forms represented in Figs. 1-9, where the 
intrusive cells are included, not within vessels, but within 
various modifications of parenchymatous tissue. The most 
conspicuous feature presented by these intrusive cells is the 
great differences in their sizes, as well as in the modes in 
which they are aggregated, even within the same host-cell. 
These differences are so great as to suggest, at the first glance, 
that we have more than one kind of object even within one 
host-cell. But opposing this conclusion is the fact that varied 
as are the forms, sizes, and groupings of these intrusive cells, 
we find every possible gradation between even the most 
distinct varieties ; hence I conclude that whatever these 
objects may be, they all belong to one type of vegetable 
organism. At the same time we cannot identify them with 
any of the thylosis. If the description of the origin and 
development of these thylosis 1 , given by Max Reess, be 
correct, they can only find their way into the interiors of 
elementary tissues whose walls are furnished with points that 
are weak because of their thinness. The vessels represented 
in Figs. 11-14 were so far scalariform as to present such areas 
of weakness, rendering it at least possible that the cells which 
they contain may be thylosis. But the walls of the parenchy- 
matous cells which contain the intrusive ones now figured, 
exhibit no indications whatever of having had any such thin 
1 See Professor M. Ward’s English Translation of Sachs’ Physiology of Plants, 
p. 581. 
