Ohap. II. BREAKING THROUGH THE GROUND. 79 



tive fact that it is not arched, as it has not to force 

 for itself a passage through the ground. In the accom- 

 panying sketch (Fig. .58) the petiole of the first leaf 

 has already partially straightened itself, and the blade 

 is beginning to unfold. The small second leaf ulti- 

 mately grows to an equal size with the first, but this 

 IJrocess is effected at very different rates in different 

 individuals : in one instance the second leaf did not 

 appear fully above the ground until six weeks after the 

 first leaf. As the leaves in the whole family of the 

 AcanthaceaB stand either opposite one another or in 

 whorls, and as these are of equal size, the great in- 

 equality between the first two leaves is a singular fact. 

 We can see how this inequality of development and 

 the arching of the petiole could have been gradually 

 acquired, if they were beneficial to the seedlings by 

 favouring their emergence ; for with A. candelabrum, 

 spinosus, and latifolius there was great variability in the 

 inequality between the two first leaves and in the 

 arching of their petioles. In one seedling of A. can- 

 delabrum the first leaf was arched and nine times as 

 long as the second, which latter consisted of a mere 

 little, yellowish-white, straight, hairy style. In other 

 seedlings the difference in length between the two 

 leaves was as 3 to 2, or as 4 to 3, or as only '76 to 

 • 62 inch. In these latter cases the first and taller leaf 

 was not properly arched. Lastly, in another seedling 

 there was not the least difference in size between the 

 two first leaves, and both of them had their petioles 

 straight ; their laminae were enfolded and pressed 

 against each other, forming a lance or wedge, by 

 which means they had broken through the ground. 

 Therefore in different individuals of this same species 

 of Acanthus the first pair of leaves breaks through 

 the ground by two widely different methods ; and ii 



