236 BIOLOGY. 



But at first the odd terminal leaf necessarily originates, 

 because a leaf must have several pairs of ribs, before it 

 splits in a ptiloidal or pinnate manner. The primary 

 number of petals is therefore one. This number is found 

 in those plants called apetalous, where the small lateral 

 petals are abortive, and frequently the terminal petal 

 itself, as in the catkin, where only the calyx has been left 

 remaining. 



1210. The normal ratio, in which the numbers of the 

 petals progress, is the odd or uneven. For a leaf is to 

 be regarded as a single fascicle of fibres with cellular 

 substance. This packet of fibres grows straight out. It 

 is solicited by the light to give off bundles of fibres ; 

 there is thus no existing cause, why it should only give 

 off such upon one, and not upon the other, side of the 

 bundle. At the first division therefore it must be an 

 odd leaflet, which is the principal bundle of fibres, while 

 two even pinnate leaflets take their origin upon its 

 sides. 



1211. The second number of petals is therefore three; 

 for this is the first number in which a pinnate leaf can 

 appear. This number is much more frequently met 

 with than the former, because all division of a terminal 

 bud necessarily strives after the representation of the 

 whorl. Under this head come most Monocotyledons, as 

 grasses, rushes, lilies. 



1212. Of the three petals of a corolla all three are not 

 of equal import, two only are alike as being lateral pin- 

 nate leaflets ; the third, however, is present as the odd or 

 uneven leaflet. 



1213. Upon this inequality of import depends the 

 irregularity of many ternary corollae, e. g. of the Orchideae, 

 Apiaceae, and even many Irides and lilies. 



1214. If the trinity or ternary division depend upon 

 the pinnated leaf, so must also the next number depend 

 thereupon. 



1215. The third prevalent number in the vegetable 

 world is the quinary. The quinary division originates, 

 when to the two pinnate leaflets two others are super- 



