412 SPHENOPHYLLALES. 
B. PSILOTACEAE 
the fertile shoot is very lax, and does not form a definite strobilus, while 
foliage leaves are interspersed irregularly between the sporophylls. There 
Psilotum triquetrum, Sw. Shoot showing repeated 
dichotomy, bearing minute toothb-like sterile leaves, and 
turgid synangia attached to the minute forked sporo- 
phylls. It is to be noted that a sterile region intervenes 
between two fertile regions. Natural size. 
is thus a ‘Sedago” condition in 
Psilotum also, and it is even more 
obvious than it is in Zmesipteris, 
Psilotum is also open to deviations 
of structure of the spore-producing 
parts: reduction of the sporangia 
from the normal three to two is 
not uncommon, though it appears 
frequently to be the result of arrest 
of one of the loculi. In other 
cases the number of the loculi 
may be increased to four or five.! 
Thus in the Psilotaceae sporangio- 
phores may be found _ bearing 
sporangia variable in number from 
one to five. The observations of 
Thomas also show” that there are 
fairly numerous instances in Ps?lo- 
tum of a second dichotomy of one, 
or even of both branches of the 
forked sporophyll: in the former 
case two  sporangiophores are 
present and three minute leaf-lobes, 
in the latter case three sporangio- 
phores and four leaf-lobes. The 
synangia are in these instances 
closely crowded together, and in 
some cases at least irregular quin- 
quilocular synangia are due to the 
fusion of two original primordia in 
close proximity. There are no 
statements as to the position in 
the fertile region which these 
abnormalities hold. From the 
above facts in Pszlotum, as well 
as those in Zmesipteris, Thomas 
draws the conclusion “ that repeated 
dichotomy of the sporophylls of 
the family Psilotaceae is an ancient 
feature.” Without accepting this position, this much at least is clear, 
that the present Psilotaceae possess morphological possibilities of further 
*Solms Laubach, dvx. Jard. Bot., Buitenzorg, iv., p. 174. 
* Proc. Roy. Soc., vol. 1xix., p. 349. 
