UNDERWOOD: AMERICAN FERNS 247 
«' unfolds and (cf. larger figure) a second fork is produced at Y 
which by successive forkings duplicates the simple condition first 
observed. The system of forks at Y may be distinguished from 
those below as forks of the second order. From Ya terminal bud 
may produce later a fork of the third order (Z) and its terminal bud 
may continue the process as long as the tissue of the main stem 
retains the power to convey nourishment. Even this condition is 
comparatively simple, if it would remain so, as it does in certain 
Species ; but in others, buds everywhere developed at the lateral 
forks as at a, a, @, a, may unroll and produce an interminable array 
of complications. A moderate example of this is shown at the 
left-hand fork above Y; from this simple example it will not be 
difficult to imagine the possibilities of complication arising in a 
vigorous upright stem. The primary branches at c, c, may be 
called the primary internodes; at d, a, d, d, we have the secondary 
internodes, and so on through the entire series of the pseudo- 
dichotomy. 
In the field it is of prime importance to get the primary fork 
in a normal condition ; in it the characters of the bud-scales and 
the extent of the decurrence of the segments on the secondary and 
Primary internodes is of great importance. Often these are both 
naked except for a casual stfpule-like segment at the bud itself; 
in others the secondary is pectinate like the upper pinnae while 
the primary is naked ; in others still the primary is pectinate on 
the inner side or in some species on both sides ; so far as we have 
been able to see, these characters are fairly constant. One species 
(D. Pectinata) presents a modification of this method of forking, 
the alternate forks producing merely a pair of pectinate pinnae, 
while the Opposite one produces a second fork of which the alter- 
Nate internode again produces a pair of pinnae, while the other 
§0es on as before, thus forming an apparently zigzag axis and 
withal most graceful sprays, as the species is vine-like and often 
Teaches a length of several meters. : 
Hooker and Baker recognized twenty-one species in their 
Gleichenia § Mertensia * (which is Dicranopteris) eight of which are 
r Synopsis Filicum ed. 2. 12,15,and 449. 1874. Besides this two of Mettenius’ 
Species published in 1864 are included in the Index and referred to p. 449 of the text, 
but no mention of them occurs on that page or elsewhere in the work. 
