20 



PRACTICAL BOTANY 



means of which plants carry on their work. Energy in the 

 form of heat is also one of the results of respiration. Respira- 

 tion may occur in the absence of free oxygen, but is more 

 complete, and thus releases more energy, when oxygen is 

 present. When respiration is complete, it results in the forma- 

 tion of various compounds, chief of which are carbon dioxide 

 and water. Carbon dioxide and water may be carried from the 

 plant through the leaf, or other parts of the plant, and the 

 oxygen supply may enter in the same way. It is evident, how- 

 ever, that the transfer of these gases is an incident associ- 

 ated with the real respiration, which consists in decomposition 

 of complex substances and the release of energy therefrom. 

 Also it is evident that, so far as respiration is concerned, plants 

 and animals behave in the same way. It should be noted that 

 in photosynthesis green plants utilize carbon dioxide, though 

 they, like other plants and animals, may produce carbon dioxide 

 as one of the products of respiration. 



21. Flowers and seeds : the parts of the flower. The flower 

 is the part of the plant by means of which seeds are produced. 



Flowers differ 



^Corolla ^W\ widely, but an 



examination of 

 any such sim- 

 ple flower as 

 that of the gera- 

 nium or the ox- 

 alis shows that 

 there are four 

 kinds of floral 

 parts in it (Fig. 

 FIG. 13. Drawings of two flowers 13).Outermost 



A, entire flower ; B, part of the floral structures removed -j i owps f j a 



set of greenish leaves known collectively as the calyx, the sep- 

 arate leaves being known as the sepals. Just above the calyx, 

 and usually larger and more conspicuous, is the corolla, each 

 leaf of which is a petal. Above the corolla is the group of 



