FASCIATION 47 



and tube collectively constituting such a corolla. The fusion 

 of stamens amongst themselves, as in Hypericum, etc., also 

 fusion of stamens to petals, carpels fused to form asyncarpous 

 ovary, all come under this head, which, according to the 

 author, accounts for the great variety of form and structure 

 met with in the plant world resulting in the varied combina- 

 tions formed by cohesion of parts, or, on the other hand, the 

 breaking up of primitive organs into a greater number of 

 parts. 



I have frequently been struck by the modification in form, 

 structure, and durability of leaves produced on the clustered 

 branches, more especially of conifers, called ' witches' brooms,' 

 caused by fungi. Do such leaves represent a reversion to a 

 more primitive type of leaf borne by the ancestors of the 

 tree? 



The following account of the origin of fasciation is given 

 by Miss Knox, who investigated the causes and transmissibility, 

 from generation to generation, of the banding or fasciation 

 of stems in the evening primroses. 



It was found that the malformations in question were due 

 to injury in all cases examined. The injuries are caused by 

 larvae which hatch and feed on the growing tips, attacking 

 the cells while still in a merismatic condition. In most plants 

 which are attacked the growing region is destroyed or its 

 vitality impaired, or the surrounding leaves alone are con- 

 sumed, the cells of the apex not reached, when no fasciations 

 result. Certain swarms of larvae, by boring into the heart of 

 the tip, inflict delicate wounds which may induce fasciation. 

 The occurrence of the phenomena is dependent on three 

 factors the individual manipulation of the insect, the extent 

 and nature of the wound, and the innate character of the 

 plant. Slow-growing species are more apt to fasciate than 

 those of rapid development. 



In the case of fasciation from the rosette stage, the injuries 

 may be made by small larvae in the soil, and usually date 

 from the first stages of germination. The development is 

 slow, and all the causes must be traced far below any sign of 

 their effect. The fasciations are ordinarily flat, but often 

 ring-.shaped, and intermediate stages between the two are 

 common. The appearance of secondary meristems, which 

 later differentiate and which may eventually become incor- 

 porated with the bundle ring, in conjunction with the altera- 

 tion of the stem's shape, is a frequent occurrence. 



