360 PRACTICAL COURSH IN BUTANY 
shows many windings and deviations from the direct route. 
The monocotyls furnish a conspicuous example of this de- 
parture from the general law of progression. It was formerly 
supposed, on account of their greater simplicity of structure, 
that they were a more ancient type than dicotyls, but recent 
investigations point to the conclusion that they are a later 
offshoot, derived from ‘some primitive form of aquatic dicotyl, 
and represent, not an ancient and primitive stock, but a case 
of retrogressive evolution from a higher type. Strong pre- 
sumptions in favor of this view are: (1) that various species 
of dicotyls show an unequal development of the seed leaves, 
amounting, in the bryony, tc complete abortion of one of 
them, while some monocotyl seeds show morphological 
characters that can best be explained as survivals, or inherit- 
ances, from a dicotyl ancestor; (2) the structural resem- 
blances between gymnosperms and dicotyls are closer than 
between gymnosperms and monocotyls, which could hardly 
be the case if the latter were the more ancient; (3) the geo- 
logical record does not show them to have appeared before 
dicotyls; (4) the number of cotyledons furnishes no criterion 
as to the relative age of any plant group, since all three types 
are represented among the pteridophytes, where plants are 
found bearing one, two, or more cotyledons. 
The theory of their comparatively recent origin from an 
aquatic ancestor is further borne out by the many points of 
similarity between their internal structure and that of hy- 
drophytes (818), and also by the great proportion of aquatic 
plants among them, amounting to thirty-three per cent, while 
in dicotyls the proportion is only four per cent. Can you 
give any reasons, from your examination of their internal 
structure (113, 114), for believing that the line of develop- 
ment which they have followed is a less effective one for 
meeting conditions now existing on the globe than that at- 
tained by dicotyls? 
We should remember, too, that while progressive evolution 
implies successful adjustment to surroundings, it is possible 
