242 ' IMANUAL OF AGPJCULTURE. 



an important influence upon the passage of water from soil to 

 atmosphere, when the immense extent of forest area throughout 

 the world is considered. Much of it, however, is retransferred 

 to the ground, having been condensed on the colder leaf surface 

 by warmer air currents. The wholesale hewing down of forests 

 has been observed to produce a scp.rcity of rain in regions where 

 no such privation existed while the forests flourished. Plants 

 by their gTeen colouring matter act as purifiers of the air by 

 aljsorbing carbonic acid, so hurtful in excess to animal life. 

 This process is accomplished by such colouring matter when 

 subjected to solar action, decomposing the acid, and whilst free- 

 ing the oxygen, assimilating the carbon. 



A flower when normally develo^^ed consists of four parts — twa 

 called the enveloping organs, viz., the calyx or outer circle, and 

 the corolla or coloured portion, and the remaining two called the 

 essential organs, as being necessary for the production of seed, 

 and named respectively the stamens, and in the centre the pistil. 

 All parts alike are modifications of the leaf. The leaves forming 

 the calyx are named sepals ; those of the corolla, petals ; and in 

 each they occur, either united or separate, and assume infinity of 

 shape. The stamen consists of a stalk or filament, frequently so 

 short as to make it appear absent, which supports two bags 

 called anther lobes, these containing a dust powder — the pollen 

 of the flower, necessary for the fertilising of the ovules or germs 

 of the embryo, and these are held by the pistil or ovary. Above 

 this last is the style or stalk, having at its extremity the 

 stigma, upon which the pollen must be deposited ere it can 

 come into contact with the ovules. The changes in the bean 

 flower may be taken to illustrate the stages of the repro- 

 ductive process. The grains of pollen on the stigma extend 

 minute processes down the style into the ovary, where, 

 coming into contact with the ovules, fertilisation ensues. ISText 

 the calyx, corolla, and stamens, having performed their functions, 

 wither and die. The pistil or ovary is now disclosed, as having 

 assumed the shape of a pod, and within it the fertilised ovules 

 have developed into a row of beans or seeds. The plants of some 

 varieties have staminate or male flowers on some of them ; pis- 

 tillate or feminine flowers on others Others bear both sexes on 

 one and the same plant ; whilst the generality bear flowers con- 

 taining both, stamen and pistil together, and these are called per- 

 fect flowers. The various modes of fertilisation in plants is an 

 interesting study ; and the unlikely agencies through which the 

 access of pollen to the ovules is effected bear evidence of the 

 highest design. Insects have a great share in this ofiice, 

 through the adherent pollen on their legs and bodies getting 

 deposited on the stigmata of the successive flowers upon which 

 they alight. Indeed, it is maintained by the most eminent 



