176 BOTANICAL GAZETTE [MARCH 
Fraxinus, Crategus, and Kornus, haustoria pierce the cells of the 
loose parenchyma in a minority of cases. Usually the intercel- 
lular hyphe first penetrate the leaf to a region intimately asso- 
ciated with the fibro-vascular bundles ( fig. 31) before producing 
absorbing organs. Sometimes haustoria are found in the cells 
between the bundles and the palisade cells, and sometimes in the 
palisade cells themselves. Palla observed hyphe passing into 
the palisade layer, but he did not find haustoria there. In 
Xanthoxylum, however, haustoria frequently penetrate the cells 
of the loose parenchyma (fig. 27.) Fig. 32 shows that the inter- 
cellular hyphe which enter the stomata are either side branches 
of exterior hyphe or the ends of original hyphe. Except when 
the interior hyphz arise as side branches immediately over the 
stomata, it is impossible to determine whether we have to do 
with an original germinating tube or not, so long as cross sec- 
tions of leaves are used. If the stoma stands wide open, the 
initial cell of the penetrating hypha is not narrowed (jigs. 27, 28), 
but upon the closing of the stoma the initial cell accommodates 
itself to the space left to it. It thus is narrow at the middle and 
becomes larger at the distal end (figs. 30, 33). Palla finds that 
the intercellular hyphe of P. suffulta contain at most three cells 
(24, p.7),and of P. Berberidis two (seldom three) more. The cells 
of the hyphe within the leaves examined by me vary with the 
distance to be traveled before the production of an absorbing 
organ. Fewer than two cells were not found. The number is 
typically three to five. The distal cell of the intercellular hyphe 
is sometimes extremely long. It is possible that, in tracing the 
sinuosities of the hyphe through several sections, septa and 
nuclei may have been overlooked which would raise the number 
of cells to more than five. When the hyphe produce their 
absorbing organs near the stomata, such hyphe are noticeably 
larger than the surface hyphe. But when the filaments extend 
a long distance through the intercellular spaces, some oF all 
of the cells are more or less attenuated (particularly the dis- 
tal cells.) An intercellular hypha may sometimes extend 
through more than a dozen sections. Haustoria do not appe@f 
