148 THE PLANT WORLD. 



signs of irregularity in the radial symmetry of the apex ; or by 

 apertures suggesting callus or a bifurcating meristem. Reddish 

 color is indicative in some species, and large numbers of these 

 ''stung tiles'' when sectioned reveal fasciation phenomena. 



The character of the fasciation induced varies widely, but 

 the forms are found together on the same plant, and the cause is 

 the same for all of them. In the adult plants it is common to 

 hnd ring fasciations and bifurcations along with the simple flat 

 bandings. (See figure 29.) Tliere are also grooved stems 

 which gradually flatten, and Avliich in the development of the 

 secondary meristems and the reinforcement of the primary 

 bundle ring are to be classed as forms related to the ring fascia- 

 tions. Certain stems begin to fasciate at a point where a cylin- 

 drical protidjerance, looking like an aborted branch, projects from 

 the axis. The protuberances are various in character, and may 

 or may not be abortions of the axis. They are sometimes mere 

 distorted projections of the surface, composed of bundle elements 

 covered with callus. They are always associated with callus for- 

 mation, and are due to the ravages of the insects. Their struc- 

 ture varies greatly, but in its more complicated form is similar 

 to that of the ring type in the occurrence of the secondary meri- 

 stems. Bifurcations ordinarily accompany them and all of the 

 forkiuffs are often fasciated. Sometimes in these bifurcated 

 stems the forks are not flat, but the stem is then banded below the 

 point of division. The histological condition of the various 

 types cannot be dwelt upon at length here, nor the structural 

 phenomena attendant upon the injuries. 



It seems not improbable that the forui of the fasciation is 

 dependent upon the localization of the injury. Stems injured 

 in the centre of the apex or irritated there may produce ring fas- 

 ciations by a spreading of the apical meristem in radial distri- 

 bution. Those injured on the side may become linear fascia- 

 tions, and a larger, wider attack of irregular kind j^roduce the 

 protuberances. The time of the attack makes a great difference 

 in the development. If the injury is to the growing region of a 

 biennial plant still in the rosette stage, the plant fasciafes during 



