SUMMARY. 



249 



discarded as inadequate. Dichotomy occurs as a 

 normal feature in certain Palms. 



The two main views as to the nature of fasciation, 

 held by past authors, viz., the " fusion-theory," and 

 the "expansion " theory, are discussed. The writer's 

 " pleiotomy "-theory is regarded as alone adequate to 

 explain the phenomenon. 



The physiological causation is briefly touched on. 



Proliferation : this is of two kinds, viz., median and 

 axillary ; the former concerns the main shoot, the 

 latter the lateral branches. The phenomenon consists 

 in an extension of the shoot beyond the limit of 

 growth which is normal to it. 



Under the main heading of Simplification are in- 

 cluded the phenomena of suppression and fusion. 

 Suppression of the main axis is the converse condition 

 to that of proliferation of the same, and is due to 

 internode-shortening and extinction. Suppression of 

 axillary shoots results in an un branched stem. Fusion 

 of two or more shoots may be either post- or con- 

 genital ; the latter is always between the main and an 

 axillary shoot, giving rise to the phenomenon of an 

 extra-axillary branch 



All the phenomena of simplification are progressive 

 and not reversionary. 



The subject of Direction of Growth includes the 

 change of direction which the stem or branches, or 

 both, may assume during their growth. Here are 

 considered : horizontal shoots, erect shoots, inverted 

 shoots, and winding shoots. The majority of these 

 changes are progressive in nature, but the vertical 

 direction of growth of the ivy-shoot and of the rhizo- 

 phore of Selaginellcc must be regarded as reversionary. 



The reason why shoots grow in this or that direc- 

 tion must be sought for in their vital needs, the action 

 of gravity being subsidiary and subsequent to these. 



Adventitious shoots are described as occurring on 

 roots, stems, leaves, in ovaries, and on prothalli. The 

 prothallus-shoots constitute the phenomenon of apo- 



