274 MONOCOTYLEDON US & DICOTYLEDONOUS LEAVES. [BOOK i. 



larger. The projection corresponds to the radicle ; the 

 excentricities become the cotyledons. 



In those leaves, the petioles of which end in a tendril or 

 an awn, the rudiment of this point of the petiole is always 

 the first to appear. 



As the rudimentary tumour of the growing leaf increases 

 in size, differences characterising Monocotyledons and Dicoty- 

 ledons are visible. In Monocotyledons it is generally found 

 that for each leaf, a rim is gradually formed around the 

 whole nucleus of the axis; this rim is a little oblique, and 

 but slightly marked on the side opposite the point of the 

 leaf ; it increases in size by the thickening of the upper edge, 

 at the same time that the summit of the leaf, with which it 

 is continuous, elongates as well, so that the whole forms a 

 sheath, closed below and open at the top.. 



In Dicotyledons, as a general rule, the rudimentary tumour 

 of the leaf increases at its base without completely surround- 

 ing the stem. When the leaves are opposite, their rudiments 

 correspond with a rim continued round the summit of the 

 axis ; from this rim arise isolated points which become deter- 

 minate parts of the leaf; in this case the completely developed 

 leaves are contiguous or grown into one another at their 

 base. When the leaves are completely distinct the one 

 from the other, the rim offers, even from their first appear- 

 ance, contractions which correspond to the points of sepa- 

 ration. When the leaves are whorled, there is formed around 

 the axis a continuous circle of small tumours, each of which 

 corresponds to the apex of a leaf. 



This first form of the nascent leaf is the same for all leaves, 

 whether simple or compound. In some orders the summit 

 of the axis is not visible at the period of the birth of the 

 leaves, (especially when these are opposite), and it is only 

 at a later period, that it rises above their base to give birth 

 to new leaves ; one might be misled in this case, and sup- 

 pose that the axis is composed of leaves which had grown 

 together. 



"Formation of a Simple Entire Leaf. This sort of leaf 



