THE STEM OR SHOOT. 



93 



finished a structure, too compact and concentrated 

 a whole to be due to a mechanical union of a number 

 of separate shoots. Every appearance afforded by the 

 phenomenon suggests a single structure in itself. 



Nestler says : 66 Fasciation cannot be a fusion of 

 several axes, but only an expansion of a single normal 

 cylindric axis which from hitherto unknown causes 

 has arisen from a peculiar modification of the growing 

 point." Takobasch believed that it arose in conse- 

 quence of an incipient forking of the stem. With 

 these views the writer fully concurs. 



c. Pleiotom //- Theory. — Moquin's definition, however, 

 does not cover the whole ground, nor fully explain 

 the phenomenon. The basic principle governing the 

 latter is expressed in the following quotation from 

 Blaringhem : " Fasciations result, not from the union 

 of yonng organs which remain coherent for a longer 

 or shorter period, but from the absence of indi- 

 vidualization of the cells or tissues into independent 

 buds. Fasciation results from a retardation in the 

 dissociation of the parts." That is, apparently, during 

 the ontogeny no fusion between two or more indi- 

 viduals has ever occurred, but where now only one 

 individual has been developed, two or more were 

 always, since the period of fertilization of the ovum, 

 potentially present, and the multiple dichotomy (actual 

 or latent) in which fasciation consists, represents the 

 imperfect formation of multiplets, just as trichotomy 

 represents that of triplets, and dichotomy that of 

 twins. 



If a vertical first division occurred in the fertilized 

 ovum, causing the separation of two distinct cells, the 

 result would be the formation of twin-embryos, as 

 observed in Rhizophora conjugata. Treub describes 

 a case in which in Loranthus sphserocarpus, the ferti- 

 lized ovum divides by a vertical wall, but the sister- 

 cells develop together into a single proembryo, con- 

 sisting of a double row of cells. The case of imperfect 

 twins, in which the lower part of the structure is 



