248 



PRINCIPLES OF PLANT-TEH ATOLOGY. 



The Root. 



The following abnormalities are crealt with : 

 Branching, including the monopodia! type, forking, 

 and fasciation. 



Fusion, post- and congenital. 



Change of direction of growth ; the primary cause 

 of this resides in the habit and needs of the plant, the 

 mechanism employed being the influence of gravity on 

 the cell- contents, which gives the necessary stimulus 

 for the movement. 



Adventitious roots, occurring on roots, stems, leaves, 

 floral organs, and prothalli. 



The Stem. 



This includes the ordinary leafy stem and its 

 branches, and the hypocotyl. 



Under the main heading of Differentiation are 

 grouped the following phenomena : 



Fasciation : of this there are two main types : 

 ordinary fasciation and ring-fasciation. The former 

 consists of a multiple forking of the shoot, which may 

 either be latent, i. e. without reaching external mani- 

 festation, resulting, in that case, in the ribbon- or fan- 

 shaped shoot, or the apex divides, giving rise to a 

 number of branches of equal rank. Ring-fasciation 

 consists of an apical invagination (congenitally-formed) 

 of the stem, thus giving rise to two concentrically- 

 grouped sets of tissues, an external, normally-orien- 

 tated, and an internal inversely-orientated set, an 

 epidermis-lined central space being formed. The 

 wdiole may subsequently become split up into two 

 or more cylindric branches, whose point of union 

 below is at the apex of the invagination. Fasciation 

 is a variant of dichotomous branching. Dichotomy is 

 defined as an apical division of the organ into two' 

 parts of equal rank, the text-book definition being 



