OF THE GENUS ULEX. 29 



Branch 4. — Seven leaves ; one to three with spines, four to 

 seven with flowers. 



Branch 5. — Ten leaves ; one to three with spines, four to ten 

 with flowers (Fig. 14), 



Branch 6. — The nearest branch to the apex with five leaves, 

 all with flowers in their axils. 



The secondary spiny branches also bear leaves with flowers or 

 tertiary spiny branches in their axils, and these appear to follow 

 the same rule. In Branch 2, for example, I found the secondary 

 spiny branches in the axils of leaves one to three, with two foliage 

 leaves, right and left at the base, and in the axils of each a spine. 

 On the secondary spines, four to eight, I found two foliage leaves 

 on each, in the same position as above, and in the axils of all 

 were flowers. On Branch 5 I found that, of the secondary spiny 

 branches, one to three, each produced two foliage leaves at the 

 base, and the third branch a third foliage leaf in addition. One 

 leaf on each of the spines numbered one and two had a tertiary 

 spine in its axis ; the other leaf a flower. On spine No. 3 the 

 two lower leaves had flowers, the upper leaf none, being only 

 very small. 



The primary spines vary considerably in length according to 

 their position, being longest on those parts of the plant which are 

 well exposed to the light and shortest on those parts which are 

 hidden by the surrounding branches. If a Furze bush be examined 

 carefully, it will be seen that the length of both primary spines and 

 secondary branches varies regularly according to the amount of 

 exposure to light, and, further, the arrangement of the various 

 primary, secondary, and tertiary spines and leaves is such that the 

 largest surface of assimilative tissue is exposed to light with the 

 smallest amount of overlapping, so that the light can filter down 

 from the higher to the lower portions of a branch without any 

 serious interruption. 



According to Wydler, two cases of leaf arrangement obtain on 

 the primary spines. In the first case, there are two leaves at the 

 base standing opposite one another, and at right angles to the 

 foliage leaf, in the axil of which the spine is borne (see Fig. 14). 

 These are followed by a leaf higher up on the branch, and on its 

 upper surface exactly midway between these two (Fig. 14). 



