198 Plants and their Ways in South Africa 



conditions, come to resemble one another in habits and 

 appearance. 



A Euphorbia is mistaken for a Cactus by many, but it 

 would be hard to find a common ancestor for these two 

 families. To be frank, however, it must be confessed that 

 authorities in botany find much to puzzle them in making out 

 the ancestral tree for the plant family where difficulties meet 

 them at every turn. 



It was formerly thought that Monocotyledons were more 

 primitive than Dicotyledons but largely from evidence afforded 

 by the vascular tissue of Monocotyledon seedlings it is now 

 quite generally held that they have been derived from early 

 Dicotyledons. However, both groups may have branched off 

 from some ancestry common to both. Other problems deal 

 with the nature of the flower. Were the first flowers provided 

 with well-developed perianths or were they inconspicuous and 

 without a perianth ? There is evidence among the fossils in sup- 

 port of both views. Has the perianth been derived from 

 modified bracts or from modified stamens? Were the first 

 flowers perfect or unisexual and were flowers first pollinated 

 by wind or were wind-pollinated flowers derived from those 

 formerly pollinated by insects ? 



Probably some of the flowers which are without a perianth 

 are primitive and some are reduced. An apetalous flower oc- 

 curring in an order where the greater number of genera have 

 petals may have lost the habit of forming petals which its 

 ancestors possessed. The same may be surmised of wind- 

 pollinated flowers. 



In the systems of classificition, the natural order Ranun- 

 culaceae will be seen to stand first in the well-known English 

 system of Bentham and Hooker. Primitive (unspecialized) 

 characters of this order are seen (i) in the indefinite number of 

 perianth segments and sporophylls (stamens and carpels). (2) 

 These are separate from one another, and (3) arranged in 

 spirals (instead of cycles or whorls) ; (4) a convex axis 

 (thalamus or receptacle). These characters, which are not 

 found throughout this order, are more clearly seen in Mag- 

 noliaceae. 



