PHYLOGENETIC AND ONTOGENETIC INTERPRETATIONS OF THE CATAPHYLL

Abstract

To many of the early students of plant morphology it seemed only natural to suppose that the organization and position of cataphylls in the shoot system indicated their derivation from foliage leaves in accordance with the need for protective organs about the bud during certain parts of the year. This assumption seemed to be well supported by the frequent occurrence of leaves intermediate in character between foliage leaves and cataphylls, a phenomenon which even at the present time is cited, especially in botanical texts, as showing that scales in reality are reduced foliage leaves. Such formal considerations, while of some pedagogical value, entirely neglect the factors responsible for the striking divergence between the scale and the foliage leaf and thereby give to the problem a static quality which has done much to discourage active investigation. Indeed, the problem of the successive and periodic development of scales and foliage leaves on the shoot is still in nearly the same stage as it was during the time of Goethe (i3), Alexander Braun (i), and De Candolle (3). The causes for this unsatisfactory state of knowledge have been examined in a recent paper by the writer (8) and the conclusion reached that at present we have no satisfactory morphological or causal interpretation of the cataphyll. This statement was made with due regard to the transformation developed by Goebel (i I, I2) and to the various phylogenetic theories of the scale as given by Velenovsk' (i8), Tyler (I7), Domin (6, 7) and Cook (4). However, at the 5th International Botanical Congress, Domin, in a re-statement of his theory of the evolution of the phyllome,2 maintained in fundamentals his previous view of the nature of the cataphyll and questioned the value of ontogeny as a method of approach to the problem of foliar morphology. It is not my purpose to analyse in detail Professor Domin's views as to leaf evolution but in the following discussion an effort will be made to show that until our knowledge of the nature of the primitive leaf in seed plants has been inductively established, the problem of cataphyll morphology can be most effectively approached by intensive developmental studies. A few facts will serve to indicate the uncertain position at the present time of phyletic theories of the scale.