422 
APPENDIX 
The midrib of a leaf or leaflet is called the costa. 
The veins and veinlets may be simple or branched. If a 
vein or veinlet runs freely above its base and does not 
connect again with another vein or veinlet, it is called 
free. Veins which unite and thus produce a closed net¬ 
work are said to be anastomosing and the venation is then 
reticulate. A free included veinlet is one which is free in 
a space or an areola enclosed by anastomosing veins. 
A compound frond is pinnate, if the leaflets are 
attached serially to a main axis called the rachis. It is 
palmate, or digitate, if the leaflets spring from a common 
point to the top of the stipe. The leaves of Marsilea, 
having four equal leaflets in the form of a Maltese cross, 
are called cruciform. The leaflets of a pinnate leaf are 
called pinnae. If these pinnae are compound, they are 
described with the use of the same terms applied to simply 
compound leaves. The leaf as a whole is then bipinnate, 
the ultimate divisions are called pinnules. If the pinnules 
in turn are compound, or twice compound, the frond is 
tripinnate, or quadripinnate. 
There are a few terms applied to pinnae, which rarely 
or never apply to whole leaves. The bases of pinnae are 
frequently oblique; that is, the pinnae are unequal-sided 
at the base. The lower side is frequently cuneate, and 
the upper side truncate. If the base of the pinnae is 
widened and the dilated part grown out to a point, the 
pinnae is said to be auricled. If the inequality of the 
sides extends throughout the leaflet, the part below the 
costa being almost wanting, while the part above it is well 
developed, the leaflet is dimidiate; the upper side of a 
pinnae, that is the side toward the apex of the frond, is 
the acroscopic side, and the lower side is spoken of as 
basiscopic. 
