6i8 



BOTANY OF THE LIVING PLANT 



This floral structure is very constant in the Grasses, but the flowers are variously 

 disposed in their inflorescences. The Rye-Grass may be taken as a good 

 example for the Family, and it is easily recognised. 



The inconspicuous flowers, versatile anthers, dry dusty pollen, and expanded 

 feathery stigmas clearly indicate wind-pollination, with promiscuous inter- 

 crossing. Most Grass-flowers are homogamous, that is, stamens and stigmas 

 mature simultaneously, but some are protogynous (Alopecurus) . 



The fruit is a dry nut, containing one albuminous seed and a lateral embryo. 

 Its structure is well illustrated by the grain of wheat or maize (Fig. 465). 



The Gramineae are the most important Family in supplying the wants of 

 man. Their fruits are the various cereal grains (Appendix B) : their foliage 

 gives fodder for animals : sugar is yielded by the Sugar Cane ; and the Bamboo 

 serves most various uses to the dwellers in the Tropics. 



DICOTYLEDONEAE. 



These Plants are characterised by the embryo bearing two coty- 

 ledons. The leaves are net-veined, usually with a narrow base, and 

 a definite petiole. The stem and root show secondary thickening by 

 means of a cambium. The flowers are usually pentamerous, or 

 tetramerous, with distinct calyx and corolla. The plants are perennial 

 or annual, many of the former developing as shrubs or trees. 



The Dicotyledons are divided into two large series, according to the 

 separateness or coherence of their petals. This distinction does not 

 serve a like purpose in the classification of the Monocotyledons ; it 

 has already been seen that the very natural Family of the Liliaceae 

 is variable in this respect. But in the Dicotyledons the same varia- 

 bility within natural families is exceptional : therefore this dis- 

 tinction serves to give a natural separation of them into Polypetals, 

 or Choripetalae, with the petals all separate from one another ; 

 and the Gamopetals, or Sympetalae, where there is a coherence of 

 the petals to form a united, usually tubular corolla. 



The former is undoubtedly the more primitive state. It repeats the 

 condition usual in the vegetative region, and it is characteristic of 

 those less specialised flowers which on many other grounds are held 

 as less advanced. The gamopetalous state is characteristic of flowers 

 which are more specialised as pollinating machines, and they may 

 therefore be held as more advanced. But there is no reason to hold 

 all plants showing gamopetaly as necessarily related to one another : 

 this would involve the assumption that the advance had happened 

 only once in the course of Evolution. It seems probable that in a 

 plurality of evolutionary lines the advance was made to gamopetaly, 

 and the student should be prepared to recognise this in any sequence 



