50 



PART I. THE MORPHOLOGY OF PLANTS. 



[12- 



degree of elongation of the epipodium. When the epipodium 

 elongates considerably, the lamina has a well-marked primary 

 axis from which more or less numerous secondary axes of growth 

 successively spring, and these in turn bear lateral axes of a higher 

 order : the resulting lamina is then of the pinnate type (Fig. 30 

 A). When, however, the epipodium remains short, it constitutes 

 merely an intercalary growing-point from which a number of 

 equal secondary axes spring, and the resulting lamina is of the 

 palmate type (Fig. 30 B}. 



The development of the peltate lamina, closely connected with 

 that of the palmate type, is effected by a peculiar form of basi-petal 



FIG. 30. A Pinnate leaf of the Beech, Fagus sylvatica ; m mid-rib, n lateral rib?. B Pal- 

 mate leaf of Alchemilla vulgnris (nat. size). C Pedate leaf of the Plane (| nat. size). 1, 2, 

 3, are the ribs or axes of the 1st, 2nd, and 3rd order. 



growth. In peltate foliage-leaves (e.g., Tropseolum, Nelumbium, 

 Hydrocotyle, Cotyledon, Lupinus, etc.) the petiole is inserted in 

 the middle of the under surface of the lamina, so that the long 

 axis of the former is perpendicular to the plane of expansion of 

 the latter. At first the development is that of a palmate leaf, 

 the petiole being inserted at the base of the lamina, and at the 

 point of insertion there is an intercalary growing- point from which 

 spring several axes (Fig. 31 B, 1,2,3) in basipetal succession. But 

 in this case the last-formed axes (4-4, 5-5, in the figure) grow out 

 in front of the petiole, with the result that the whole lamina 

 gradually comes to lie perpendicularly to the petiole. 



