A P P E N D I X. 79 
fmaller plant, are fufficient at all times to diftinguifli 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 hap¬ 
pened, had a ftridl regard been had to the frudlification in both. 
In the Polypodium thelypteris, the feed-veffels are arranged in clofe 
regular lines, along the margin of the lobes ; at firft of a pale colour, 
changing brown in the progrefs; and, after the difcharge of the feeds, 
fpread out in breadth fo as to occupy the whole dilk, except the middle 
only ; this, however, is not always the cafe, for in fome fpecimens the 
lines remain diftinft and feparate to the laft ; and in thofe moft effedlually 
covered, the difpolition and arrangement of the feed-veffels, in marginal 
lines, remain viiible. 
But in the fpecimen of Acroftichum thelypteris now before me, which 
is in a middle ftate of growth, and is accurately figured, T^ab. 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 of the nerve ; fome are 
further advanced in growth than others; and the whole difk, 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 the whole under fide, except the margin only, is clofely 
covered with fmall feed-veffels, and they originate in every part of the 
difk, as in the genus Acroftichum, not in regular lines or rows, as in 
Polypodium. Fig. a. in Tab. 44, is a fingle lobe magnified. 
The barren leaves. Fig. b, were in a ftate of half growth in the fpe¬ 
cimens I examined ; after the decay and fall of the fecond leaves, the rib 
of the firft leaf turns brown, and abides on the root over winter. 
R 
POLYPODIUM 
