October 21, 1904.] 



SCIENCE. 



527 



this case the axis would be from the first 

 the predominant part. 



Tlie first of the above alternatives, viz., 

 that the prototype of the leaf existed from 

 the first, and was indeed the predominant 

 part in the initial composition of the shoot, 

 has been held by certain writers as the basis 

 of origin of the leafy shoot in vascular 

 plants.* On this view not only is the 

 whole shoot regarded as being mainly com- 

 posed of leaves, but some even contend 

 that the axis has no real existence as a part 

 distinct from the leaf bases, f 



This view in its general form represented 

 the plant as constructed on a plan some- 

 what similar to that of a complex zoophyte. 

 It has more recently culminated in the 

 writings of Celakovsky and Delpino. The 

 former in his theory of shoot-segments 

 ( ' Sprossgiiedlehre ' ) starts from the posi- 

 tion that the plant is composed of morpho- 

 logical individuals; the cell, the shoot and 

 the plant stock are recognized as such. 

 The stock is composed of shoots, and the 

 shoot of cells. Braun recognized the shoot 

 as the individual par excellence; between 

 the cell and the shoot is a great gulf, which 

 has not yet been filled; 'between the cell 

 and the bud (shoot) there must be inter- 

 mediate steps, the limitation of which no 

 one has succeeded in defining'; the long 

 sought for individual middle step is the 

 shoot segment (Spross-giied), which is 

 neither leaf only, nor stem segment only, 

 but the leaf together with its stem segment. 

 Now this appears to me to be purely Pla- 

 tonic morphology; the intermediate step 

 must occur ; we will, therefore, discover 

 and define it. The definition of it consists 



* Goethe. ' Die Metamorphose &er Pflanzen.' 

 Gaudiehaiid, Mem. de I'Acad. d. Sci., 1841. 

 Kienitz Gerloff, Bot. Zcit., 187.5, p. 55. Celakovsky, 

 ' Unters. ueber die Homologien,' Pringsh. Jahrb., 

 XIV., p. 321, 1884; Bot. Zeit, 1901, Heft, v., VI. , 



t Delpino, ' Teoria geiierale della Filotassi.' 

 For ref. see Bot. Jahresbr., VIII., 1880, p. 118, 

 also Vol. XI., 1883, p. 550. 



in the drawing of certain transverse and 

 longitudinal lines partitioning the shoot, 

 lines which in the sporophyte have no ex- 

 istence in nature ; the assumed necessity of 

 partitioning the shoot into parts of an in- 

 termediate category between the whole 

 shoot and the cell brings these assumed 

 limits into existence. 



Notwithstanding the ingenuity of the 

 theory as put forward by Celakovsky, in 

 the absence of any structural indication of 

 the limits of the shoot segments in the vast 

 majority of cases the theory does not ap- 

 pear to me to be sufficiently upheld by the 

 facts. 



An extreme, and indeed a paradoxical 

 position has been taken on this phytonic 

 question by Delpino. As a consequence 

 of his studies on phyllotaxis he concluded 

 that the axis is simply composed of the 

 fusion of the leaf bases ; that the leaves are 

 not appendicular organs, but central or- 

 gans; that an axis or stem system does not 

 exist, and accordingly that the higher 

 plants are not eormophytes at all, but 

 phyllophytes. There will, I think, be few 

 who will adopt this fantastic view of the 

 shoot. 



The second view, that the axis and leaf 

 are the result of differentiation of an in- 

 different branch system, of which the limbs 

 were originally all alike, has lately been 

 brought into prominence by Potonie.* 

 Taking his initiative from the branching 

 of the leaves in early fossil ferns, he recog- 

 nizes the frequent occurrence of overtop- 

 ping ('Uebergip felting'), that is, the grad- 

 ual process of assertion of certain limbs of 

 a branch system over others ; in the branch- 

 ing of fucoids he finds an analogy for his 

 observations on fern leaves, and draws the 

 following conclusion, that 'the leaves of the 

 higher plants have been derived in the 



■* ' Lehrbueh d. Pflanzenpalaeontologie,' pp. 156- 

 159. Also ' Ein Bliek in die Geschichte d. Bot. 

 Morph. und d. Perioaulomtheorie,' 1903, p. 33, etc. 



