THE SYMMETRICAL CONCENTRATED TYPE. 147 



rise at first, culminating in a maximum at the 13th node, with a 

 gradual fall towards the slender apex ; the whole shoot being of a 

 spindle shape in the bud and the leaf members approximately 

 constant in volume. 



The leaves at successive nodes were as follows : — 



11, 13, 14, 14, 17, 20, 20, 22, 24, 27, 28, 29, 30 ; 29, 30, 26, 26 ; 

 26, 23, 23, 21, 19, 16, 14, 12, 9, 8, 6, 6, 4, 3. 



The number thus ultimately falls to 3, which possibly represents 

 the ancestral number derived from the three segments of the apical 

 cell, as in the similarly constructed apex of the leafy gametophyte 

 axis of many mosses; although it is difficult to prove, even in 

 Equisetum, that since the protuberances which indicate the prim- 

 ordia appear to involve these segments, they are necessarily 

 dependent on the histological segmentation. 



Another strong shoot (May 1901) including 40 internodes gave 

 similar results : springing from a rhizome of uniform construction 

 with 13 members in a whorl, the shoot reached the level of the 

 soil in 5 internodes, 13, 13, 16, 18, 22 respectively ; the maximum 

 was reached in 12 internodes, the additional ones being 24, 27, 28, 

 30, 33, 34, 36 respectively. As in the previous example, this 

 maximum condition was succeeded by a region in which variation 

 took place, the numbers for the next 5 nodes being 34, 36, 32, 34, 

 35. A steady descent then set in and was continued for the 

 remaining 23 nodes :— 36, 34, 32, 30, 30, 30, 29, 27, 26, 24, 24, 22, 

 20, 17, 14, 12, 9, 6, 5, 5, 4, 4, 4. 



Uquisetum, Telmateia thus affords an excellent example of the 

 possible independence of each nodal-formation of a symmetrical 

 system ; the bulk-ratio is independently arranged for each cycle 

 of members, and although it may remaia constant when only a few 

 large primordia are inserted, the curious oscillation period between 

 the rising and falling series shows that in the case of relatively 

 very small primordia the mechanism is imperfect and only 

 approximates the number at each node. Similar phenomena occur 

 in the Dasycladaceae (Neomeris) ; in Equisetum they become the more 

 striking, in that very regular constructions are often postulated for 

 the stelar system, which is only secondary to that of the leaves, 

 and thus less accurate than is generally supposed. 



