86 



PRINCIPLES OF PL ANT-T K R ATOLOGY. 



within the body of the parent axis and which have not 

 as yet given rise to individually distinct axes; this 

 unbranched condition is well seen in the fan-shaped 

 type of fasciation met with occasionally. 



Precisely the same phenomena, viz., of dichotomy 

 and fasciation, which are generally abnormal in the 

 Phanerogams, occur normally in the Cryptogams. 

 In Lycopodium, e.g., dichotomy constitutes almost the 

 only method of branching of the stem, the main body 



Fig. 25. — a. Fasciated shoot of pine. (After Masters.) b. Portion of 

 thallus of the Alga Halidrys siliquosa. 



of which divides into two equal parts. Again, dicho- 

 tomy and both types of fasciation, viz., the band- and 

 fan-shaped varieties, occur in the thalli of Algse and 

 Fungi (fig. 25 a and b). Such a structure of the 

 thallus can also be regarded as a latent condition of 

 multiplex forking which in many cases resolves itself 

 at the apex of the thallus into actual forking.* 



The mechanical causation of the phenomenon may 



* All the phenomena above considered are merely variants of a single 

 one, viz., dichotomous branching, of which the two extreme forms are, 

 respectively, simple forking and the band- or fan-shaped undivided fascia- 

 tion. The cases of multiple forking, which link these two extremes together, 

 may be separated into two classes : (1) those in which the apical branching 

 is successive (each newly-formed branch forking subsequent to its forma- 

 tion), and (2) those in which it is simultaneous (the forkings, few or numerous, 

 arising congenitally as such). In (1) the forking occurs at different levels ; 

 in (2) at the same level. 



