THE STEM OR SHOOT. 



91 



apical invagination (what the Germans term "Einstul- 

 pung") of the organ, comparable to the turning inside 

 out of a glove-finger, as is indicated by the fact that in 

 most cases the cavity ends blindly before reaching the 

 base of the organ, and, as in such instances as the 

 mummy pea and the dandelion, by the terminal aper- 

 ture. This is the morphological explanation of the 

 phenomenon ; as the formation of the cavity by this 

 means is congenital, there is, of course, no indication 

 thereof in the ontogeny. This will at once explain the 

 set of inverted tissues adjacent to the cavity. If now 

 we imagine a number of pairs of constrictions to occur 

 (each pair consisting of a constriction on the outer and 

 one on the inner surface), the tissue between the pairs 

 of constrictions rounded off, so that the normally- and 

 inversely-orientated parts of each such region become 

 one cylindric whole (see the diagrams, fig. 26), a number 

 of subsidiary terminal shoots will be produced, as in 

 the mummy pea or the dandelion described by Reich- 

 ardt. The innermost of the three vascular rings 

 ascribed by him to the central of the five fused scapes 

 might belong to a tissue representing the resurgence 

 of the downwardly-invaginated scape-tip. 



The two internal scapes, occurring side by side, 

 found by Michelis in the dandelion, could be explained 

 by the presence of tw^o apical invaginations. Adven- 

 titious proliferation of the stem within the base of the 

 scape is the probable explanation of the instance in 

 which Michelis observed a third capitulum-bearing 

 scape within the others, as it probably also is of other 

 similar cases mentioned in the literature. 



Rrng-fasciation is thus seen to be a A^ery remarkable 

 method of effecting a dichotomy of the stem. 



Causes of Fasciation. — As regards the causes under- 

 lying the phenomena of fasciation, two main views on 

 the subject have been held. 



a. Fusion - Theory. — Some authors, e.g. Linnaeus 

 (" Fasciata dici solet planta cum plures caules connas- 

 cuntur, ut unus ex plurimis instar fasciae evadat et 



