150 RELATION OF PHYLLOTAXIS TO MECHANICAL LAWS. 



II. . . 15 



T. Ti- T"- Till- Tiv. TV- Tvi. 



I" 



11 11 



12 12 12 11 11 10 



12 11 



III. . . 14 



12 12 11 11 



12 13 12 12 



12 12 11 



tl2 13 11 13 



the reduction being thus fairly progressive from 15 to 10 along the 

 ultimate ramifications. 



The case of Equisetum further illustrates the mechanism of 

 addition and loss of members. No rules are here applicable ; the 

 number added may be quite irregular, and in the case of falling 

 symmetrical phyllotaxis, the amount of adjustment required in the 

 mechanism must be very considerable. So marked is the rising and 

 falling sequence in the vegetative shoot of E. Telmateia, and so 

 relatively short is the region over which a constant phyllotaxis 

 would be possible, that it may be said that this plant never possesses 

 anything better than an irregularly symmetrical construction ; the 

 obvious part of the whorled appearance being produced by the 

 adjustment of the secondary zones of growth which constitute the 

 internodes. The apical portion of such a plant may be taken as a 

 type of " irregular symmetry," which is again a distinct phenomenon 

 from normal asymmetry, but, as will be seen, incapable of distinction 

 as a primary phyllotaxis construction from irregular asymmetry. 



Taking the latter example of ^. Telmateia* anA translating it into 



* It will be noticed that this aflfords what may be termed an architectural 

 conception of the Equisetum shoot, based on the view that all the leaf members 

 are of equal value, and that Equisetum is only a modern highly xerophytic 

 edition of a plant which once presented normal vegetative leaves ; on the other 

 hand, it does not accord with the accepted versions of the construction of the 

 apex of such a shoot, usually found in text-books, the older researches on this 

 plant having been conducted from the standpoint of the dominant influence of 

 the aj)ical cell (Hofmeister, Eeess, Cramer). Once this cell is deposed from 

 authority, it wUl be seen that it is extremely difficult to prove whether the 

 annular ridge really belongs to a cycle of three segments which have been " a little 

 displaced" (Keess), or may not equally well be regarded as the result of an 

 independent symmetrical annular impulse which must nearly approximate these 

 superficial cells. The same annular ridge again represents such an early gamo- 



