THE LEAVES 



45 



the margins of the two nerves : the lower part is colourless. The prophyll 

 grows usually to a length of an inch or more and is inserted on the lateral 

 shoot in such a position that its flattened side is turned towards the axis 

 from which the shoot arises. The first foliage leaf, however, which suc- 

 ceeds this prophyll has a divergence from 

 the latter of 90 only, to the right or left, 



A 



FIG. 35. Tip of the coleoptile with first foliage 

 leaf emerging, i, Front; 2, back view. 



so that it and subsequent leaves which 

 follow the ordinary rule of 180 diver- 

 gence from each other are arranged in a 

 plane at right angles to the foliage leaves 

 of the preceding axis (Figs. 37, 38). 



This is the normal arrangement of the 

 leaves upon stems and lateral shoots in 

 practically all grasses as first indicated by 

 Godron. 



In the bud the leaves are convolute, 

 the blades being rolled up from one 

 margin to the other. The rolling alter- 

 nates from leaf to leaf, one in which the 

 right margin is folded over the left being 

 followed normally by another in which 

 the left margin covers the right. The first foliage leaf of the embryo 

 above the coleoptile is not, however, always rolled from the same side ; 

 in some plants the right margin is folded over the left, in others the 

 opposite arrangement occurs (Fig. 36). There are therefore two forms 

 of plants which may be termed respectively " right- " and " left-handed," 



FIG . 3 6 . Young plants . i , " Right - 

 handed " ; 2, " left-handed " ; A 

 and B, transverse sections of the 

 shoots i and 2. 



