\'oL. 43 T O R R E Y A July 1943 



Leaf-stem Relationships in the Vascular Plants* 



Ralph H. Wetmore 



It is an arresting fact that in the year of our Lord 1942 there is still no 

 general agreement on the organization of the Vascular Plants. Perhaps the 

 nearest one can get to a generalization is the admission that Avascular Plants 

 ordinarily comprise root systems and shoot systems. Studies of the shoot 

 s}'stems indicate the usual presence of stems, leaves and reproductive parts. 

 The interpretation of the relation of leaves to the stem which bears them has 

 been varied. From time to time there have been those who adhered to the 

 phyton hypothesis, a hypothesis that made the leaf the important unit of con- 

 struction of the shoot system, each leaf consisting of the foliar appendage 

 and its subjacent stem segment or internode. This concept by which the stem 

 becomes a vertical aggregation of leaf bases was probably advocated first by 

 Gaudichaud in 1841. and subsequently by Schultz (1843) and by Delpino 

 (1880, 1883). Little of really scientific contribution could be attributed to 

 these workers. Their fanciful ideas, however, were given an artificial bolstering 

 l)v Celakovsky ( 1901 ) when he brought toegether a group of serious arguments 

 supporting the foliar nature of the stem. However, as Schoute (1931) points 

 out these same facts upon which Celakovsky's arguments were based could 

 equal!}' ^^•ell be explained otherwise. This early hypothesis did not have a 

 large or literal following. No more did Chauveaud's phyllorhiza hypothesis 

 (1921) a modification of the phyton concept, meet with general acceptance. 



Alternative ideas, which held the stem to be an independent organ bearing 

 foliar appendages, have been prominent and generalh' much more in favor. 

 Our textbooks bear witness to this fact. 



AMth these two concepts of the shoot system in mind, I should like to 

 present the results of certain recent and current developmental studies. Since 

 the work of Buder (1928) and his students (Schmidt, 1924, etc.) on apical 

 meristems there has grown a body of knowledge \vhich challenges the form- 

 alized interpretations of developmental patterns in the apices of root and 

 shoot attributed to Hanstein (1868). These studies have been continued 

 especially by the significant works of Schiiepp (1926) and Foster (1935, 1936, 

 1938, 1939a, 1939b, 1940, 1941a, 1941b). The latter investigator has made 

 progress on a comparative study of the diverse types of apical meristems in 

 different plant groups. The already classical works on Helm (1931, 1932) 

 and Louis (.1935) have extended our knowledge of the whole stem tip 

 with its developing leaves. ]\Iore recently numerous workers have contributed 



* Read at the 75th Anniversary Celebration of the Torrey Botanical Club at Columbia 

 University, ^vlonday, June 11, 1942. 



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