434 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



Winteraceae are remarkable for the retention of the one-pored grains in a per- 

 manent tetrad (Bailey and Nast, 1943a, 1945a), a characteristic which Robert- 

 son believed to be linked with insect pollination. The pollen of Euptelea fluctu- 

 ates between monocolpate and tricolpate, as does that of some members of 

 Ranunculaceae and Berberidaceae (Nast and Bailey, 1946). In view of the 

 frequently suggested affinity between Ranales and Alismatales, it is noteworthy 

 that AVodehouse (1936b) and Erdtman think the peculiar polyporate pollen of 

 Alismataceae might be derived from that of Ranunculaceae, although Butomus 

 has monocolpate grains. Moseley sought to derive the acolpate, triporate pollen 

 of Casuarina from a basically tricolpate condition in Ilamamelidaceae; Erdtman 

 tends to relate most of "the Amentiferae" on pollen structure. 



Wodehouse contends that the various forms of pollen grain of angiosperms 

 "have all been derived from each other by evolutionary processes" (1936a, p. 

 67). He quotes Fischer to the effect that the general trend has been toward a 

 simultaneous strengthening of the outer spore wall, and the formation of pre- 

 arranged exits for the pollen tube (1935). Adaptation to wind pollination leads 

 to a progressive thinning and smoothing of the exine, until all anemophilous 

 grains tend to resemble each other, irrespective of origin (Wodehouse, 1931, 

 1936a). Entomophily, on the other hand, frequently leads to an accumulation 

 of oil in, and the marked adornment of, the outer spore wall, as especially well 

 shown in Compositae (Wodehouse, 1931, 1935, 1936a). A suggestion that a ratio 

 exists between size of pollen and length of style, indicating a phylogenetic trend 

 toward decrease in spore size, has been offered by Covas and Schnack (1945). 

 In his new book, Erdtman confines himself to "an interpretation of the deflection 

 of the 'palynological compass needle' " (1953, p. 27), but his suggestions of pres- 

 ence or absence of affinity between many families makes fascinating study. AVith 

 the probable exception of the significant distribution of monocolpate pollen and 

 the specialized nature of that in "the Amentiferae," Erdtman's restraint seems 

 to be entirely appropriate and to set the limits beyond which, as yet, we are 

 scarcely prepared to go. 



D. Significance of emhryological characters: The foregoing extremely sketchy 

 discussion of the embryological features of angiosperms gives point to the quali- 

 fication of Maheshwari that "the embryologist would however be glad to admit 

 that he lays no claim to erect a phylogenetic scheme of his own" (1945, p. 32). 

 We can perhaps agree with Just: 



Embryological data need not be accorded more recognition than other taxonomically 

 valuable characters. They do, however, deserve their rightful place among the others, a 

 position they have not yet attained in the eyes of all botanists (1946, pp. 354-355). 



If currently available information on the ovule and the gametophytes does not 

 permit the erection of unique phylogenies, it does provide a whole galaxy of new 

 characters. Many of those of possible taxonomic utility have been summarized 

 by Netolitzky, Tischler, Schnarf, AVodehouse, Just, Maheshwari, and Erdtman. 

 Of particular relevancy is the advocacy by Schnarf, Maheshwari, and Just of 

 embryological diagrams and formulae, so that as many features as possible 

 may be compared in determining relationship. 



As we have observed to be the case with other anatomical characters, the re- 

 sults are frequently negative. The differences between two taxa may be so mani- 

 fold that it seems unlikelv that they bear any close relationship to each other 



