330 



HUTCHINSON'S POPULAR BOTANY 



We approach more interesting ground when we begin to speak of the 

 expanded flower. The question of form and arrangement again meets us 

 on the threshold, but the study of the structural variations of flowers by 

 110 means confines one to the acquisition of name -lists or to tedious and 

 meagre definitions. The question is one of scientific importance, involving 

 as a preliminary step the arrangement of multitudes of appearances under 

 primary points of view, and their classification according to rule and 

 exception ; by which means alone a discovery of the actual laws of Nature 

 is rendered possible. Now, manifold as are the structural arrangements 

 of flowers, the variations really concern only a few simple subjects, and 

 when these are grasped the investigation of the causes which produce 

 the differences in the whole floral world is by no means a hopeless under- 

 taking (Schleiden). 



The subjects of variation are, in fact, four; and 

 the first to be mentioned is number. A Lily, for 

 example, has three sepals, three petals, and six 

 (i.e. twice three) stamens ; while its pistil, though 

 looking like a single organ, is really made up of 

 three carpels which have grown together. The 

 Lily belongs to the great class of Monocotyledons, 

 and three may be said to be the characteristic 

 number of that class. In the floral whorls of 

 Dicotyledons, on the other hand, threes are a 

 rarity ; nor can any number be said to be charac- 

 teristic, though fours and fives are very common. 

 A Fuchsia has four coloured sepals, four petals, 

 twice four (i.e. eight) stamens, and four carpels. 

 A flower of Cherry, on the other hand, has its 

 two outer whorls, the calyx and corolla, in fives, 

 and its stamens form a multiple of five namely, 



twenty. The ovary does not follow the rule it is solitary ; nor is this case 

 by any means an exceptional one, the parts of the pistil in the majority 

 of Dicotyledons being fewer than in the other whorls. 



It might easily be shown that whorls of flowers correspond to cycles 

 of leaves, but it would be exceeding our present limits to push our inquiries 

 farther in this direction. 



The second of the four subjects of variation is cohesion. This term is 

 applied by botanists to the union of like parts in a flower, as of sepal with 

 sepal, petal with petal, stamen with stamen, and so forth. Both the calyx 

 and corolla of a Primrose are good examples of cohesion. Here the five 

 sepals unite in a tube and form what is called a gamosepalous calyx ; the five 

 petals are also fused together, and so the corolla is described as gamopetalous.- 

 A calyx whose sepals are not united is said to be polyseptdous ; a corolla 

 with separate petals is polypetcdous. In the Laburnum (L. vulgare) the fila- 



Fia. 401. COMMON PEA. 



A carpel with seeds removed. 



