305 



2. E. selom Schau., and E.ferruginea Schau. Leaves all opposite, sessile, cordate, rather obtuse or 

 acute. The branches and axis of the inflorescence provided with rusty-brown felt or bristly hairs. Small 

 trees in tropical north-east Australia, reaching southward as far as 20°. Both species remind oi.e 

 somewhat of Angophora, and are related to the next species : — 



3. E. perfoliala R.Br. Leaves all opposite, connate in pairs, glaucous. A large shrub of the dry 

 tropical north-west of Australia. 



(p. 97). '1. E. macrocarpa Hook. All over with a glaucous bloom. Leaves all opposite, sessile, 

 with a cordate base. Flowers solitary, sessile, very large. Shrubs of considerable size in the interior of 

 south-west Australia, where it occurs in gravelly-sandy soil, with a rainfall of about 10 cm. (15| inches). 

 The only near relation of this species is E. piriformis Turcz., with mature leaves, which occurs in still drier 

 regions. There are forms of this which deviate from the typical E. pyriformis in the direction of E. macro- 

 carpa. Some have some opposite leaves, others have a white bloom, at least on the inflorescence, and the 

 pedicels, normally very distinct, are occasionally wanting. To be brief, one sees that E. pyriformis and 

 E. macrocarpa are sisters with helicomorphic distinctions in the vegetative organs. 



It must be noted that not all Eucalypts are so heteroblastic as these mentioned here. There are 

 many whose juvenile leaves differ only in size and in a broader, less falcate blade. Such juvenile forms 

 will behave in a similar way as the extreme heteroblastic forms. Therefore it canpot surprise us to find 

 amongst the normal flowering species some which make an impression of juvenility by their broader and 

 larger leaves. Amongst the S23ecies I have observed myself I have specially in mind E. Prcissiana Schau., 

 and E. grossa F.v.M. Both inhabit edaphic dry localities in south-western Australia in the dry inland 

 region. Their juvenile leaves are strongly built and xeromorphic. 



It is unfortunate that Diels has chosen the comparative examples of E. Risdoni 

 ans E. amygdalina, the relations of which have been misunderstood by both Bentham 

 and Mueller. When I deal with affinities, I shall show that E. Risdoni is nearer to 

 other species. . 



At the same time these pairs, illustratively cited, do not fundamentally affect 

 , Diels's arguments. E. amygdalina and E. Risdoni cannot be accepted as belonging 

 to the same species according to any modern criterion. Diels further quotes Mueller 

 as comparing E. ■pulverulenta and E. melanophloia and also E. Stuartiana and E. crebra, 

 two so-called Apples, with two Ironbarks. These two pairs are so distant from each 

 other in phytogenetic relations that Mueller has misled Diels, and while I think Diels's 

 generalisation is so useful that I propose it as a law. I think these particular examples 

 unfortunate. I will state the law. 



Definition of Diels's Law. 



At p. 92 Dr. Diels says, " A vegetative juvenile form and a vegetative full-grown 

 form can exist in a single species, and each form flowers and fruits, and forms a perfectly 

 closed cycle of life/' I call this Diels's Law. 



C. K. Barnes (the present work, Part XLTX, p. 27L) puts it this way : " The 

 thesis of the book is that the generative maturity of plants is not connected immutably 

 with a definite stage of their development, as has been so widely held." 



The italics are mine, and Diels's law may be conveniently expressed in that 

 way. 



H 



