10 WILD FLOWERS 



which the plant requires. (2) The Stem bears the leaves and 

 flowers, holds them in advantageous positions, and carries to 

 them water and various nutrient material. (3) The Leaves re- 

 ceive from the root water and mineral substances, and from the 

 air the important gas Carbon dioxide; from these they are able 

 to build up the food of the plant such substances as sugar and 

 starch. This they do by virtue of their green colouring-matter, 

 which absorbs a large quantity of light, necessary for the carry- 

 ing on of the chemical processes involved in the formation of 

 the food substances. (4) The Flowers have as their special 

 function the reproduction of the plant by means of seed-forma- 

 tion. In reality the flower is a collection of leaves, deeply 

 modified to enable them to perform their new work ; some 

 produce the true reproductive bodies the pollen-grains and 

 the ovules others protect these, and aid them in various ways. 



For our present purpose it is necessary to consider the ex- 

 ternal form only of these different parts : a fuller treatment of 

 their structure, and of the way in which they carry on their 

 work, is to be found in another of the books of this series, 

 Dr. Marie Stopes' Modern Botany. 



1. The Root. Only in comparatively few cases does the root 

 present features of value for the identification of a plant ; of 

 interest are those roots, which serve to store food, and so be- 

 come swollen and tuberous (e.g. orchis). 



2. The Stem. It may be necessary to note whether the stem 

 is branched or without branches simple. Many stems stand 

 straight up erect; but frequently we meet with plants the 

 stems of which lie along the ground prostrate; in yet other 

 cases the stem may support itself on external objects climb or 

 ramble. 



3. The Leaf is typically divided into two parts, the leaf-stalk 

 and the blade; very often, however, there is no stalk, and then 

 the leaf is said to be sessile. The margin of the blade is some- 

 times quite smooth entire but usually it is cut into or notched 

 in various ways. If it presents a series pf little teeth pointing 

 forwards, like those of a saw, it is serrate; if the teeth are more 

 irregular and point outwards, it is toothed. Often the cutting 

 is much more profound ; it may go right down to the central 

 vein (mid-rib) of the leaf, so dividing it into a number of 

 smaller leaflets, in which case we have a compound leafj as 

 opposed to a simple leaf one in which the cutting does not 

 reach the mid-rib. If the cutting, though not deep enough to 

 form a compound leaf, yet divides it very deeply, we have a 

 segmented leaf ; if the cutting is" less marked still, the leaf is 

 said to be lobed. In compound, segmented, and lobed leaves 

 the cutting may take place in two different ways : (1) if the 



