52 



PRINCIPLES OF PLANT-TERATOLOGY. 



organ into two would occur. But what has clearly 

 happened in the past is that the invagination, on 

 reaching the centre, widened out, the gap connecting 

 this wide, central portion with the exterior then became 

 closed, and the peripheral tissues, florets or leaves, of 

 the organ once more continuous, so that a circular 

 space was left in the centre with the orientation of all 

 the parts lining it, of course reversed. This condition 

 we find stereotyped in the various cases of "ring- 

 fasciation " met with. It appears congenitally as such 



Fig. 77. — Diagrams of " ring-fasciation." I. A single lateral invagi- 

 nation. II. Later stage, showing central cavity which is lined by 

 bracts and ray-florets. III. Three cavities formed by three in- 

 vaginations ( = stage towards trifurcation. IV. Two invaginations. 

 V. Bifurcation caused by two invaginations, from opposite points, 

 meeting in centre. 



with, as a rule, no indications as to how it was brought 

 about. Intermediate stereotyped stages connecting 

 this one with actual forking Lave not been observed, 

 although it is highly probable that such occurred in the 

 past. If ordinary dichotomy were to succeed this stage, 

 a connection between the central space and the peri- 

 pheral part of the structure would take place on two 

 opposite sides. Multiple dichotomy would result from 

 a number of invaginations, instead of one or two only, 

 which would meet and fuse in the centre (see the 

 diagrams, fig. 77). 



The phenomenon of " ring-fasciation " is frequent 



