REDUCTION OF LEAFLETS 179 



that the Orange leaf is not simple, but is really a com- 

 pound leaf having only one leaflet. 



The reason for this curious structure is a little diffi- 

 cult, but we can see that by the rachis being broadened 

 and by the branches being green, the area of green 

 tissue exposed to the light is increased so that more 

 assimilation can be done, while being thicker and 

 tougher in nature, the broad petiole is less likely to 

 suffer in an extra day or hot wind, than would ordinary 

 leaflets. 



If the leaflet is held up against the light, a number 

 of light spots will be seen. These are globular drops 

 of oil (enclosed in special glands) which, being trans- 

 parent, show white against the dark green tissue. 

 The smell and bitter taste of this oil prevents animals 

 eating the leaves, and the latter are also protected by 

 thorns. But the axillary shoots here are not short, 

 perhaps because the oil renders that unnecessary. 



PARKINSONIA ACULEATA, L. 



The branches are green, and have short stiff thorns, 

 half an inch long. From the sides of these thorns 

 spring (generally four) pinnate leaf -like organs. These 

 have each a well marked pulvinus, a broad rachis, 

 and numerous small elliptic leaflets. At the base 

 of the thorn are two small marks or scars, and if we 

 examine the youngest portion of the branch, we shall 

 see that these are the scars of small pointed stipule- 

 like scales. Just above the thorn is a small bud. 



Since there is no leaf-scar just below the thorn^ 

 it cannot be of a branch nature, while the stipules on 

 the sides and the minute bud in the axil, point to its 



