ORGANS OF REPRODUCTION. 



43 



of common flowers, to thick and firm, as in the magnolia ; 

 or fleshy, as in stapelia. In odour too they vastly difi*er, 

 the violet and rose presenting a strong contrast with the 

 Stapelia and Aristolochia, 



Flowers are called regular, when all their respective parts 

 are equal in size and form, as in the primrose, apple, phlox, 

 potato, &c. ; irregular, when the parts of the corolla difi'er 

 in size and shape, as in the violet, tropseolum, pea, fleur- 

 de-luce, and orchis families. They are termed single, or 

 uniform, so long as they retain the special forms, posi- 

 tion, and number common to the whole of the plants of 

 the species, wild or cultivated. Double, when by culti- 

 vation or some hidden cause one or more of the parts 

 change, as when the stamens and pistils become peta- 

 loid, which change or metamorphosis gives rise to the 

 beautiful double flowers of our gardens — as the wall- 

 flower, ranunculus, poppy, pseony, pink, carnation, rose, 

 &c. Sometimes regular flowers become irregular ; this 

 is known as pelorism, of which the common toad-flax is 

 an example ; as also the erect flowering varieties of 

 Gloxinias. 



In many plants the corolla is absent, the flower then 

 being called apetalous — that is, without petals. The 

 presence or absence of calyx and corolla aff'ords charac- 

 ters for dividing a great class of plants into three divi- 

 sions. First, those without calyx or corolla are called 

 achlamyds, without a covering, as the birch, willow, 

 and oak families. Second, with a true calyx, mono- 

 chlamydsj one covering ; of which the Marvel of Peru, 

 sweet bay, mezereum, nettle, dock, and amaranth are 

 examples. Third, those with calyx and corolla com- 

 plete, dichlamyds, which is common to the majority of 

 flowering plants. 



