GROUP IV. PHANEROGAMIA : ANGIOSPERM^ J MONOCOTYLEDONES. 537 



the Valley (Convallaria majalis), they describe a curve which is 

 more or less parallel to the margin ; the weaker veins usually run 

 at right angles between the stronger ones. In the Scitammese 

 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 Avoids, in Paris 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 gynseceum. Thus the typical 

 formula is IiCn, On, Jn + n, 6?n, where n in 1 most cases = 3, more 

 rarely = 2, 4 or 5. 



Lateral 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. Juncaceas) ; more rarely those of the external whorl 

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

 Alismacea3). 



This type is most closely adhered to in the Liliaceae. 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 Scitamineae 

 and Orchidacece, 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 from the Liliaceous type of flower occur among the 

 Araceae, and in the Glu males, and Typhaceae, and in certain water- 

 plants (e.gr. Naiadaceae, Lemnaceae). On the other hand, the 

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

 members of the gynaeceum and to some extent of the androecium 

 (e.g. Alismaceas). 



