THE BUCKTHORN FAMILY 239 



Genus Discaria. 



About 14 species, of which 1 is found in New Zealand. Much branched, 

 almost leafless, usually thorny shrubs, with twisted interlacing stems. Branches 

 grooved. Leaves J in. -J in. long. Flowers axillary, fascicled, small. Petals 0, 

 or 4 or 5. Stamens 4 or 5. Fruit a dry hard drupe. (Name from the Greek 

 signifying a disk, from the ovary being situated on a broad disk). 



Discaria toumatou {TJie Wild Irishman). 



A spinous bush, sometimes 20 ft. in height. Flower J in. in diameter, white ; 

 calyx, downy. Leaves, when present, fascicled or solitary in the axil of 

 spines. North and South Islands. Fl. Dec. -.Jan. Maori name Tumatakuru. 



Xerophytic Leaves. 



It doubtless sometimes happens, that, owing to slow move- 

 ments of the earth's crust, the climate of a plant habitat 

 alters. There is reason, for example, to believe that, at some 

 past time, the climate of the Canterbury Plains, and perhaps 

 of other parts of New Zealand, was much more arid than it 

 now is. Under changing circumstances, a plant has either to 

 accommodate itself to its new environment, or give place to 

 other and better adapted species. There are many ways in 

 which a plant can adjust its leaf to the conditions of a 

 desert climate. The leaf may be set obliquely to the sun, 

 as in Eucalyptus ; it may provide itself with water-storage 

 apparatus, as in Mesembrijanthemum ; the leaf margins may 

 be recurved, as in Olearia virgata ; the total leaf surface 

 may be reduced, as in many Veronicas ; or again, the leaves 

 may become spinescent, as in AciplujUa. If all these 

 methods fail in protecting the transpiring surface sufficiently, 

 the plant may become leafless. Then the stem has to 

 take on the functions of a leaf, as in CarmicJiaelia, Clematis 

 qfoliata, etc. 



Now Discaria has nearly been reduced to these straits to 

 prolong its existence. Such extreme measures, however, are 

 only adopted by the plant, if other devices for protection against 

 drought fail, or are irnavailable ; for a stem cannot be expected 

 to carry on the work of assimilation as efticiently as a leaf. 



