Metaphyta Ranunculus. 185 



the addition of new wood and new bast to that already 

 formed. The secondary layers of wood and bast arise from 

 a fascicular and interfascicular cambium, which lies internal 

 to the pencambium, and, owing to the position of the two 

 parts of the primary strands, winds in a sinuous mariner out 

 and in between the primary masses of bast and the primary 

 masses of wood. The cambium first makes its appearance 

 opposite the bast portions of the strands. 



Leaf. The arrangement of the fibro- vascular strands in 

 the dicotyledonous leaf differs from that of the monoco- 

 tyledon in being netted or reticulated, the strands starting 

 from one or more chief ribs, and gradually becoming smaller 

 towards the leaf edge, branching and anastomosing as 

 they go. 



The shape of the leaf as a whole is most varied. We 

 may distinguish, however, between simple and compound 

 leaves, and reduce each leaf or leaflet (if compound) to one 

 or other of the three types, circular, elliptical, and ovate. 

 The shape of the leaf is always related to the arrangement of 

 the leaves on the stem (phyllotaxis). It must be remem- 

 bered that the main object of phyllotaxis is to enable the 

 leaves to get a maximum of light and air. We will first con- 

 sider one or two of the chief phenomena of phyllotaxis and 

 then it will at once become apparent that the shape of the 

 leaf and the phyllotaxis are closely correlated (Lubbock). 



There are two chief methods of leaf arrangement, 

 namely, where the leaves are arranged in pairs opposite to 

 each other or in circles or whorls of more than two, and they 

 are arranged in an alternate or spiral manner round the 

 stem. These two methods may be termed the verticillate 

 and the spiral respectively. The verticillate is often 

 mimicked by the spiral when the internodes of the latter are 

 very closely approximated, as, for instance, on the floral axjs. 

 There are many varieties of the spiral arrangement, but all 

 are found to obey a definite law, viz. that if the numerator 

 of a vulgar fraction indicate the number of times it is neces- 



