408 Morphologie und Teratologie. 



distinct; and 2. positive d^doubiement, or branchin g 

 of an Organ or tissue which was primarily a unity. 



There are two kinds of negative d^doublement: a) post- 

 genital, real, or mechanical, e. g. the syngenesious 

 anthers of Compositae, and b) congenital or ideal, in 

 which fiision or cohesion occurs before the birth or onto- 

 genetic origin of the organs or tissues concerned; as nor- 

 mal examples of this latter the author cites the androecium of 

 Cyclanthera (consisting of 5 stamens) and the ovary of Primii- 

 laceae (consisting of 5 carpels), and gamopetalous corollas, etc.; 

 as an abnormal example he cites a flower of Forsythia virl- 

 dissima Lindl. in which the 2 large lateral petals represent 

 the 4 of the normal flower. 



As examples of positive dedoublement he cites the 

 „double flowers" of Rose and Daffodil; flowers of Crociis, Iris, 

 Tiilip, and many Dicotyledonous flowers in which extra members 

 occur in the various whorls; the vegetative shoot of Lonicera 

 bearing more than 2 leaves in a whorl, as representing ab- 

 normal cases of this category ; and the flowers of Lythnim 

 and Paris (which are 6- and 4-merous respectively) and the 

 pappus of Compositae as representing normal instances of 

 the same. 



The phenomenon of „fasciation" which comes under the 

 author's third heading: „Neutral condition", is identical, if 

 regarded from the ontogenetic point of view, with post- 

 genital positive dedoublement, but from the phylogenetic 

 Standpoint much more is involved. 



The phenomenon consists, briefly, in this: „that the organ 

 or tissue, at its first origin an integrity, becomes later branched 

 or subdivided in its upper or younger region". The 

 great underlying principle may be expressed thus: „that the 

 structure represents the result, final product, or compromise of 

 the strife woged between two opposing forces or tendencies, 

 viz. : „that which, on the one band, makes for fusion or inte- 

 grity, called „negative dedoublement", which is the younger; 

 and that which, on the other band, makes for Separation or 

 pluraiity of parts, or „positive dedoublement", which is the 

 older of the two, None of the structures Coming under this 

 head can be the result of either of those two tendencies acting 

 alone, for they are clearly intermediate in character between 

 the two sets of structures which were described under 1 and 2". 

 This is a) the „ideal" or „m o rp hological" explanation of 

 the phenomenon. 



The b) „mechanical" or „real" cause of the latter may 

 be ascribed to the presence of multiple growth-centres 

 at the apex of the organ which usually tend to be grouped 

 in a line; the unequal growth in length of the quasi-inde- 

 pendent organs which are fhe products of these separate centres 

 gives rise to the appearance of twisting (usually seen in fas- 

 ciated shoots). Dichotomy is due to the presence of two 



