K N D I X, 79
fmaller plant, are fufficient at all times to diftinguiih it from that ;
though a refemblance in habit and external appearance has caufed the two
fpecies to be confounded together. This, however, could not have happened,
had a ftriél regard been had to the fruftification in both.
In the Polypodium thelypteris, the feed-veflels are arranged in clofe
regular lines, along the margin of the lobes ; at firft o f a pale colour,
changing brown in the progrefs ; and, after the difcharge o f the feeds,
fpread out in breadth fo as to occupy the whole diik, except the middle
only ; this, however, is not always the cafe, for in fome fpecimens the
lines remain diftinét and feparate to the laft ; and in thofe moft effe£tually
covered, the difpofition and arrangement of the feed-veffels, in marginal
lines, remain vifible.
But in the fpecimen o f Acroftichum thelypteris now before me, which
is in a middle ftate o f growth, and is accurately figured. Tab. 43 , Fig.
a, fome of the feed-veffels are vifible, as is expreffed at Fig. c ; they are
fmall, white, and placed irregularly on each fide o f the nerve ; fome are
further advanced in growth, than others ; and the whole diik, when a
little magnified, appears befet with fmall tubercles, under which other
feed-veffels, yet in embrio, are lodged.
In the full grown plant, of which two fecond leaves are figured. Tab.
44, on Plate 4 5 , the whole under fide, except the margin only, is clofely
covered with fmall feed-veflêls, and they originate in every part o f the
diik, as in the genus Acroftichum, not in regular lines or rows, as in
Polypodiuin. Fig. a. in Tab. 44, is a fingle lobe magnified.
The barren leaves. F ig. b, were in a ftate of half growth in the fpecimens
I examined ; after the decay and fall of the fecond leaves, the rib
o f the firft leaf turns brown, and abides on the root over winter.
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