1905] BRIEFER ARTICLES 421 
into one is simply and sufficiently explained by the necessity of reduction 
in the green parts of the seedling, and that this explanation of course 
requires that the ancestral cotyledons should be acting as green assimilating 
organs above ground during the period of fusion, and excludes my first 
suggestion that they fused as sucking organs within the 
at my argument was obscure in a more important respect I infer 
from Mr. Lyon’s statement that the evidence on which it is based could as 
well be read backwards as forwards; in short that the facts on which I 
rely might be used to prove the derivation of dicotyledons from monocot- 
yledons. My statement of the argument must have been very defective 
if it admitted of any doubt on this head. No observer dealing with that 
evidence at first hand could hold such an opinion. He would find the 
evidence incomplete; he might rate its value much lower than I do; but 
so far as it goes he must allow that it points in one direction—the derivation 
of the single from the double cotyledon. To make this clear, the nature 
of the evidence must be taken into account. It is of three kinds: anatom- 
ical, embryological, general. 
The anatomical argument is due to Professors QuEvA and JEFFREY.4 
Both have pointed out that the vascular structure of the young stem in 
monocotyledons is of the exogenous or dictoyledonous type. They both 
conclude that monocotyledons are derived from dicotyledons. No botanist, 
I believe, has denied the facts, which I could confirm if necessary. Their 
theoretical value may be discounted, but the most ingenious critic could 
hardly use them to prove the descent of dicotyledons from monocotyledons. 
The embryological evidence rests primarily on my conclusion that a 
certain type of vascular structure in the cotyledon and hypocoty] of liliaceous 
seedlings is primitive, and that various other types of seedling structure 
in the same family are genetically connected with it. Where we find a 
single line of related structures there is nothing—in the absence of inde- 
pendent evidence—to show which of the extreme forms is the more primi- 
tive. But where—as in this case—there are several distinct lines of descent 
ending in the same vascular type, it is fair to assume that type as the primi- 
tive structure. For a common ancestor naturally gives rise to divergent 
stocks, but it would be an extraordinary series of coincidences which 
should lead several distinct types of structure to produce remote descend- 
ants of a single ty 
It is true that uniform conditions of life do lead to great superficial 
resemblance between organs which are morphologically distinct. But 
4 Quéva, C., Contributions & l’'anatomie des Monocotyledonées, p. 147. 1899 
Jerrrey, E. C., in Courter and CHAMBERLAIN’s Morphology of Angiosperms, 
P- 316. 1903 
