370 EQUISETALES 



organism, as is clearly seen in the case of such species as E. pratense 

 (Fig. 192). In other species again the development or non-development 

 of the branches differentiates the vegetative axes from those which are 

 fertile, as in E. aruense and maximum : in others the lateral branches 

 on fertile axes are only delayed in their development, as in E. palustre 

 and sylvaticum : in others again there is little difference as regards branching 

 between the fertile and sterile shoots. But it has been shown experimentally 

 by Goebel 1 that even in so pronounced a case of the absence of lateral 

 branches as the fertile axis of E. arvense the development of green lateral 

 branches could be induced : this was done by culture of the lower 

 internodes in a moist chamber, when green assimilating branches were 

 put out from the nodes, as in the vegetative shoot. The apparently 

 branchless fertile shoot was thus brought into line with the ordinary 

 branched type prevalent in the genus. Such facts indicate that the 

 branched condition was probably common for the genus, but in certain 

 cases a late differentiation has arisen between the colourless fertile shoots 

 where the branches are dormant, and the branched green assimilating 

 shoots. 2 



The fertile strobilus of Equisetum is normally terminal on the axis, 

 and is usually borne on the relative main axis only. Many cases exist, 

 however, of the development of the strobili on lateral branches : this may 

 be normal for certain species, such as E. myriochaetum, Cham, of the 

 sub-section Pleiostachya, Milde, well shown in Engler and Prantl, Pflanzen- 

 familien, i., 4, Fig. 343, p. 547 ; but it also occurs occasionally in others, 

 where a single terminal strobilus is normally present ("forma polystachya"}? 

 In the case of Equisetum sylvaticum polystachyum (Fig. 194), where 

 numerous lateral branches normally sterile bear small strobili, Luerssen 

 has been able to correlate the change with external conditions : 4 this is 

 the next step to bringing its determination within the limits of experiment. 

 On the other hand, numerous cases have been recorded of the continued 

 growth of the strobilus, at its apex, with a return to the ordinary vegetative 

 characters. Such facts show that the lateral branches are not essentially 

 different from the relative main axis, as regards the final end of spore- 

 production : also, that there is no absolute barrier between the vegetative 

 and the fertile regions in Equisetum. Speaking generally, the fertile strobilus 

 is not restricted to axes of any definite order. Thus it requires no great 

 effort of imagination to see in the shoot-system of Equisetum the result 

 of amplification of a simple unit, the shoot, composed of axis and successive 



^ Ber. d. Deutsch. Bot. GeselL, 1886, p. 184. 



2 For an interesting discussion of the biological relations of the sterile and fertile shoots 

 in living species of Equisetum, see Goebel, Organography , vol. ii., p. 501. 



3 For records of such developments in European species, see Rab. Krypt. Flora, iii., 

 p. 622, etc.; and especially Luerssen, " Beitr. z. Kenntn. d. Flora, W. and Ostpreussens," 

 Bibl. Bot., 1894, Heft 28. 



*L.c., p. 13. 



