184 



SCIENCE. 



[N. S. Vol. XXII. No. 554. 



THE IMPORTANCE OP INVESTIGATIONS OF 

 SEEDLING STAGES.^ 



The selection of the title, ' The Importance 

 of Investigations of Seedling Stages,' for 

 presentation before the Section of Vegetable 

 Morphology of the International Congress 

 carries with it the suggestion that it is the 

 intention of the writer to epitomize the recent 

 attempts made to solve the problem of the 

 phylogeny of Monocotyledons by reference to 

 the anatomy of seedlings. The importance of 

 these investigations is beyond question and 

 the unexploited nature of the field has never 

 been better expressed than by Miss Sargent, 

 whose name occupies the most important place 

 in these discussions, when she remarked that 

 while theoretically the embryo should offer 

 characteristics of unusual taxonomic impor- 

 tance, the only character so far of recognized 

 value seems to be that employed in the separa- 

 tion of the two great divisions of the Angio- 

 sperms. 



But this work has already been brought to 

 the attention of botanists by foreign and 

 American writers and I speak of it only inci- 

 dentally in passing to the consideration of 

 some other, though related, points, omitting, 

 of necessity, many interesting and suggestive 

 illustrations which would require far too much 

 space for their adequate discussion. 



The recent revival and defense of the con- 

 ception of the cotyledon as homologous with 

 the nursing foot of the lower forms rather 

 than with foliar organs has suggested many 

 problems which will require a broad compara- 

 tive study of all embryonic stages for solution. 



The functions performed by the cotyledons 

 are various, the protection of younger em- 

 bryonic regions, the deeper planting of the 

 young seedling, and above all, elaboration, 

 storage and absorption of food material, or in 

 other cases the cotyledons are merely vestigial 

 structures. If it be maintained that the co- 

 tyledon is homologous with a more primitive 

 nursing foot and that the Dicotyledons are de- 

 rived from the Monocotyledons by a bifurca- 

 tion of an originally simple member, the whole 



^ Read before the International Congress of Arts 

 and Science, St. Louis Exposition. 



series of adaptive modifications of the cotyle- 

 don must be studied and arranged in series in 

 agreement with their origin. 



This presents problems of no mean magni- 

 tude, physiological and morphological, the 

 solution of which demands the accumulation 

 of a vast series of comparative data. Not 

 only do the differing degrees of physiological 

 specialization and morphological modification 

 of the cotyledon among Monocotyledons offer 

 problems of interest and importance, but the 

 evolution of epigean and hypogean cotyledons 

 in the dicotyledons must be more satisfactorily 

 traced. If the close resemblance of many 

 cotyledons to foliar organs is merely similar 

 structural adaptation to the same physiological 

 function, the problem is not solved, but the 

 point of view is simply changed, since the 

 origin of such adaptations offers a group of 

 knotty problems which will require pains- 

 taking research for their solution. If the 

 cotyledons of many Onagracese are the homo- 

 logues of haustorial organs, what is the nature 

 and action of the ' correlation ' which de- 

 mands that the portion of the cotyledonary 

 lamina interpolated after exposure to the 

 light shall have a structure and venation in 

 close agreement with that of the true leaves 

 which follow rather than with the simple 

 form and tissue of many other cotyledons 

 which are photosynthetically active for a long 

 time. 



If, on the other hand, the old and generally 

 accepted view is considered the correct one 

 and cotyledons are regarded as foliar in na- 

 ture, the series of forms is almost as puzzling 

 ajid as much in need of broad and comparative 

 investigation and arrangement. 



The moriDhology of the cotyledon has been 

 called into question through a consideration 

 of the relationship of Monocotyledons and 

 Dicotyledons. Apparent transitions from one 

 great group to the other have been discovered. 

 These apparent transition stages have been 

 used to support two antagonistic views of the 

 relationship of the two great groups. It is 

 apparent that the special data so far secured 

 are very meager and, if it exists, the connec- 

 tion between the two great groups must be 



