Physiology of the Germs Cttscuta. 1 1 3 
well-cleared sections of a young haustorium in the thick cor- 
tical parenchyma of a fairly large, fleshy stem, of I mpatiens 
will show that the course of events is as follows 1 . A papillate 
cell at the tip of the haustorium becomes, by its growth in 
length, closely applied to the wall of a parenchyma-cell. By 
the pressure produced by more growth the tip is flattened 
against the opposing wall and becomes slightly enlarged. 
Presently the wall of the parenchyma-cell becomes gradually 
thinner and more incurved within the circular line described 
by the flattened tip of the pressing haustorial cell (see 
PI. VIII, Fig. 8). When the haustorial papilla first comes 
into contact with the wall of the opposing parenchyma-cell, 
one can plainly distinguish the two walls from one another 
without the aid of staining agents ; but by using a solu- 
tion of the chlor-iodide of zinc the walls of the two cells 
become differentially stained. The wall of the cortical paren- 
chyma-cell may be thicker than that of the haustorial cell, 
and may for this reason be more intensely stained ; but 
besides this difference in quantity of colour, one sees also 
a difference in quality, for the cellulose of the younger papil- 
late-cell becomes red purple, rather than blue purple, as the 
other does. When, however, the tip of the haustorial cell has 
been for a time pressed and thereby flattened against the wall 
of the parenchyma-cell, and the wall of the latter has begun 
both to bend and to grow thinner at the point of contact, the 
most careful staining and examination under a high magnify- 
ing power fail to reveal any line separating the two. The 
two walls, by the partial solution of that of the parenchyma- 
cell at least, and, I think, of that of the papilla also, have 
become fused into one (Fig. 8). Finally, by the combined 
action of solution and pressure, the tip of the papillate haus- 
torial cell enters the cavity of the parenchyma-cell, pushing 
the protoplasm and nucleus to one side in some cases (Fig. 9), 
or more commonly penetrating, but otherwise not disturbing 
the protoplasm in any way. Furthermore, as Fig. 10 shows, 
the haustorial papilla becomes fused, at the region where it 
1 Compare pp. 307, 308 and figures i6 a , i6 b , and i6 c in my former paper. 
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