234 THE SCOTTISH BOTANICAL REVIEW 



2. All but a few of the families and orders (6) have been recog- 

 nised in a fossil state, and most of these in the I'ertiaries. 



3. The group appears to have diverged from the primitive Angio- 

 spermic stock, evolved from a line of ancestors connecting Pterido- 

 sperms, Bennetti tales, and eventually such dicotyledons as Magnolia, 

 Liriodendron, Nymphcea, and the monocotylous Alismacese and 

 Liliaceae. 



4. There is every appearance of reduction in the floral symmetry, 

 but the characters of the cotyledons, stem, and leaves are apparently 

 as primitive as those of the primitive dicotyledons — further than which 

 latter they have not progressed. The uniform aquatic habit would 

 account for a great deal of this in stem and leaves, and even cause 

 some reduction. In other words, monocotyledons are retrogressive 

 and dicotyledons progressive types. 



5. The prevalence of aquatic, geophytic, and climbing genera lends 

 support to the view that they are a weaker or degraded race of 

 Angiosperms which have sought refuge in aquatic habits, thus avoid- 

 ing the severer struggle for existence upon land. 



6. The view is held that the difference in cotyledons is due partly 

 to the shape of the embryo-sac and supply of endosperm, partly to 

 the mode of life of the plants after germination. 



7. The stem structure is due to physiological causes, since the tree 

 type is more or less absent, and where present traces of a cambium 

 often occur. 



8. The absence of any recapitulation during the ontogeny of 

 monocotyledons of a supposed previous dicotylar stage is regarded 

 as conclusive evidence that the former are not derived from the 

 latter. 



9. It is held that the primitive Angiosperms resembled an 

 Alismaceous or Liliaceous type, on the one hand, and a Ranalian 

 type on the other, and that the monocotyledons and dicotyledons 

 are divergent series from a common ancestor, recalling the common 

 characteristics of the two as the one or the other were called into 

 being by either physical or natural selection. In the one case, 

 dicotyledons, there has been progression and differentiation; in the 

 other, monocotyledons, retrogression and even some reduction from 

 a common ancestor of the primitive Angiospermic type. 



