476 



EVOLUTION OF THE EUCALYPTS, 



hitherto found them uniform throughout, though there may be 

 sHght differences in size, vigour, etc. tStill, knowing that hybrid- 

 ism has actually been proved in the genus Acacia (Proc. Linn. 

 Soc. N. S. Wales, xxxv., Pt.2), of which, as of the Eucalypts, so 

 many species occur in Australia, we may hope soon for actual 

 demonstration of such occurring in the latter. Up to the present, 

 though much lias been said as to one species being a hybrid of 

 two others, we have had no actual proof. 



Fruits and Seeds. — In Eucalyptus, the fruit is a capsule open- 

 ing at the top in three to six valves, which dehisce along their 

 centre. In E. phcenicea, there are only two cells. Fruit generally 

 many- seeded, the majority, or all but one, being sterile. In the 

 cori/mbosa-grouip, of which E. corymhosa may be taken as the 

 type, there is generally only one fertile seed to each cell, and 

 this is vertically compressed, and flattened from before back- 

 wards, the hilum showing as a paler depression in the middle of 

 the ventral surface, and the testa is frequently prolonged into a 

 membranous appendage to aid distribution by the wind. In E. 

 corymhosa^ the posterior angle is keeled. In most of the other 

 Eucalypts, the fertile seeds are more luimerous, and are com- 

 pressed and angled laterally, according to their position in the 

 cell: the hilum is at the narrower inner extremity, and the larger 

 outer extremity is rounded to the shape of the wall of the cell. 

 The sterile seeds are light brown, narrow or linear, the fertile 

 ones dark brown or black. 



The testa is membranous, brown or black, and has not under- 

 gone much modification, except in the development of the afore- 

 said membranous appendage in the Corymbosas, and some allied 

 northern species. 



Endosperm is absent. 



Embryo. — As endosperm is not present, the form of the embryo 

 depends on the shape, size, and manner of folding of the coty- 

 ledons. The length of the petioles in the embryo depends on 

 the distance from the junction of lamina and petiole to the 

 superior pole of the radicle; and, in most species, is probably 

 fairly short before germination. In E. citrwdora and E. macn- 

 lata, the cotyledons are almost sessile. In E. marginata, the 



