CONSTANCE: SYSTEMATICS OF THE ANGIOSPERMS 447 



are primitive features. The ^dea that the iHonocotyleduus, because many of their 

 orders are sharply distinctive, must have had greater time to allow for more ex- 

 tensive dechnation, was advanced l)y \on Tuzson. McNair concluded that evi- 

 dence from the comparative biochemistry of seed fats and other organic com- 

 pounds indicates that monocots are both simpler chemically than dicots and 

 older in terms of phylogeny. AYorsdell was led to his preference for the monocots 

 as the older group by adherence to the Phyton theory, and Domin (1931) by his 

 Phyllome theory. The seniority of dicotyledons over monocotyledons, on the 

 other hand, has been accej^ted on various kinds of evidence by llenslow (1893, 

 1911), Sargant (1902, 1903, 1904, 1905, 1908), Ilallier, K. Fritsch (1905, 1932), 

 Hill (1906), Arber and Parkin, Lignier (1908), Lotsy (1911), Bessey (1915), 

 Chamberlain, Suessenguth, Parkin, Sprague, Ankermann, Bews, Hutchinson, 

 Zimmermann, Cuenod (1932), Ponzo (1932), Worseck, Copeland (1940), Werth, 

 and Gaussen. 



To the earlier workers, the problem of relationships of the two great classes 

 of flowering plants was nearly identical with that of the number of their seed- 

 leaves. Lyon (1905) and Worsdell (1908) considered the single seed-leaf of 

 monocotyledons to be homologous, not with any foliar structure, but with the 

 haustorial "foot" of bryophytes, and that the dicotylous condition resulted from 

 bifurcation of an originally solitary, terminal cot^dedon. Sargant found ana- 

 tomical evidence to convince her that dicotyly was the original condition, because 

 Liliaceous seedlings showed traces of bilateral symmetry. For those who re- 

 garded paired, foliaceous cotyledons as a primitive attribute, it was reasoned 

 that the monocotylous condition might have arisen either by syncotyly (Sar- 

 gant, 1903, 1904, 1905, 1908; Arber and Parkin, Suessenguth; Ponzo, 1929) or 

 by heterocotyly, through simple suppression of one cotyledon (Henslow; Coulter, 

 1915; Boyd, 1930-1931; Winkler, 1931) or by conversion of one cotyledon into 

 an haustorial organ (Sargant, 1902; Hill) or the first foliage leaf (Bugnon, 

 1931). Bancroft (1914) has pointed out that asymmetrical syncotyh' normally 

 occurs in dicot seedlings only if they come from exalbuminous seeds; thus, by 

 analogy, Alismatales would have to be primitively unilaterally symmetrical, Lili- 

 ales bilaterally symmetrical. These facts, he thought, would necessitate the con- 

 clusion that unilateral symmetry, and Alismatales, are primitive for monocots, 

 or that bilateral symmetry, and Liliales, are primitive, or that monocotyledons 

 are diphyletic. Engler insisted that monocotyly and dicotyly are of equal value 

 unless both conditions occur together in closely related plants. Noting the spo- 

 radic appearance of pseudomonocotyly in distantly related families of dicoty- 

 ledons, Suessenguth suggested that true monocotyly may have arisen repeatedly 

 and polyphyletically. According to Maheshwari (1950, pp. 429-430) : 



There are no essential differences between the monocotyledons and dicotyledons as 

 regards the development and organization of the male and female gametophytes and the 

 endosperm, and the process of fertilization is the same in both the subgroups. Further, 

 the differences in the organization of the embryo are not fundamental, for there are 

 some dicotyledons in which only one cotyledon develops fully and the other becomes 

 arrested, and some monocotyledons in which both cotyledons develop equally. 



Although monocots have probably been regarded by most workers as a mono- 

 phyletic group once its origin had taken place, there has been no dearth of 

 dissenting opinions. Thus, at least a diphyletic origin was supported by Hill, 



