BRITISH FLOWERING PLANTS 



The stem is called sinuous when it curves 

 backwards and forwards, jointed when it is inter- 

 rupted at the nodes, as in Grasses, winding when 

 it supports itself by other objects, as in Hops 

 and Beans, climbing when it supports itself by 

 thorns or aerial roots (Climbing Rose, or Ivy), 

 clasping when it attaches itself by tendrils (Red 

 Bryony, or Vine), erect when it rises straight, like 

 the trunk of a tree, decumbent when it rests on 

 the ground or rises obliquely (Mountain Pine), 

 recumbent when it rests on the ground without 

 rising (as in some species of Eubus), and creeping 

 when it clings to the ground by roots (Strawberry). 



Leaves 



It is not sufficient for the sustenance of plants 

 merely to absorb water and other liquid nutriment 

 through the roots, but it is also necessary for them 

 to breathe air, and this is the principal function of 

 the leaves. The green colour of plants is due to a 

 peculiar substance called chlorophyll, which, under 

 the influence of warmth and sunlight, absorbs from 



the surrounding air the gases required for the use 

 of the plant. But plants (except fungi and other 

 low plants, in which chlorophyll is not found) 

 breathe in the opposite way to animals, for animals 

 absorb oxygen to aerate their blood, and exhale 

 carbonic acid, which, in quantity, is poisonous to 

 them ; whereas plants require carbon for building 

 up their tissues, and therefore absorb the carbonic 

 acid from the air, and exhale oxygen. Thus, 

 during the day, plants greatly assist in purifying 

 the air which animals breathe ; but at night this 

 process is somewhat reversed, for while it is 

 necessary to their life for animals to breathe day 

 and night, in plants the function of chlorophyll 

 ceases at night, and any superfluity of carbonic 

 acid which has been inhaled during the day is 

 then exhaled. Consequently, it is not healthy to 

 allow many plants to remain in a sleeping-room at 

 night. But just as chlorophyll is wanting in some 

 low groups of plants, so is it present in the Hydra 

 and in some other low forms of animal life. 



Leaves vary much in form, and are usually 

 attached to a branch or stem by a stalk or petiole. 



