480 PART IV. CLASSIFICATION. 



The venation of the leaves is characterized by the fact that the 

 weaker veins do not usually project on the under surface. In 

 linear leaves, and in such as are inserted by a broad base, the 

 stronger veins run almost parallel ; in broader ones, e.g. Lily of 

 the Valley (Convattaria 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 Scitamine* 

 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 Paris quadrifolia, etc. (see 

 p. 39). 



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 En, Cn, An + n, Gn, where n in most cases 3, more 

 rarely = 2, 4 or 5. 



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.g. Alismacese). 



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 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 reduc- 

 tion from the Liliaceous type of flower occur among the Aracese, 

 and in the Glumales, and Typhacese, and in certain water-plants 

 (e.g. Naiadaceae, Lemnacese). 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. 

 Alismaceae). 



