38 MacDougal. — Symbiotic Saprophy tism . 
scales in a network. The scales are crescentic in cross- 
section with a row of simple fibrovascular bundles near the 
inner side. The parenchymatous tissue is provided with 
occasional large intercellular air-spaces. The scales on the 
lower part of the stem are furnished with a number of 
stomata on the outer or lower surface. Higher up these 
organs are replaced by trichomes of the simpler types found 
on the stem, which also extend to the pedicels and sepals. 
Conclusions. The absorbing organs of Pterospora have 
undergone a very great degeneration, and reduction in size. 
The investing mycelium appears to be encroaching upon 
the tissues of the root by entering the epidermal cells, in 
which it differs from Monotropa and Sarcodes. The under- 
ground stem of Pterospora has undergone such changes that 
it would be impossible to replace the roots by stem- 
mycorhiza in case of further degeneration of the roots, 
a fact which may lead to the final extinction of the species 
because of the saprophytic habit. The alteration of the 
shoot has resulted in the loss of the chlorophyll-habit, and 
the reduction of the leaves. The retention of the probable 
original size of the axis and of the large inflorescence has 
been accompanied by an adaptation of the epidermal layers 
for the conduction of water, the use of the large medulla 
as a reservoir for water, and the retention of the transpiratory 
mechanism. It is to be noted that Pterospora is the only 
dicotyledonous plant without chlorophyll, beside Cotylanthera , 
that is furnished with stomata. The small size of the shoot 
of the latter shows that no correlation can be traced between 
the bulk of the shoot and the presence of the stomata. It is 
much more probable that the matter is due to the habitat. 
General Conclusions. 
The independent saprophytes comprise organisms that 
have undergone certain adaptations whereby complex food- 
substances may be used. The necessary adaptation may 
be principally of the absorptive mechanism, or it may entail 
