GROUP IV. — PHANEROGAMIA : ANGIOSPERMJ: ; MONOCOTYLEDONES. 537 



the Valley {ConvaUaria majalis). they describe a curve which is 

 more or less parallel to the mar<^in ; the weaker veins usually run 

 at right angles between the stronger ones. In the Scitamineae 

 and a few other plants, a number of parallel transverse veins are 

 given off at various angles (sometimes acute, and sometimes nearly 

 right angles) from the midrib. Reticulate venation of the leaves 

 is unusual; but it occurs in Aroids, in Faris quadrifolia, etc. (see 

 p. 56). 



The flower of Monocotyledons consists typically of five alternat- 

 ing and isomerous whorls, two belonging to the perianth, two to 

 the androecium and one to the gynaeceum. Thus the typical 

 formula is Kn, Cn, An + n, Gn, where n in most cases = 3, more 

 rarely = 2, 4 or 5. 



Latei-al flowers have a posterior prophyllum ; hence the first 

 perianth-leaf is anterior. The perianth-leaves are generally all 

 much alike, and petaloid in both series : sometimes they are all 

 sepaloid (e.g. Juncaceae) ; more rarely those of the external whorl 

 are sepaloid, those of the internal petaloid (e.y. Commelynaceae, 

 Alismaceoe). 



This type is most closely adhered to in the Liliacece. The simplest 

 departure from it- is exhibited in the suppression of the inner 

 whorl of stamens in the Iridaceae, and in the inferior position of 

 the ovary. This latter character occurs also in the Scitaminese 

 and Orchidaceae, which are further characterized by the zygomor- 

 phism of their flowers and the considerable reduction of the 

 androecium. Other various and considerable deviations by re- 

 duction fi-om the Liliaceous type of flower occur among the 

 Araceae, and in the Glumales, and Typhaceae, and in certain watei'- 

 plants (e.g. Naiadaceao, LeranaceaB). On the other hand, tho 

 deviation may be due to increase iu number, more especially of the 

 members of the gynaeceum and to some extent of the androecium 

 (p.g. Alismaceas). 



^i^' 



