SUMMARY 395 



It has been seen in the Lycopods that the root is constant neither in the 

 time nor in the place of its appearance : it has been also seen that it 

 originates in the epibasal region in Lycopodium and /.\w/V.v, but in Selaginella 

 in the hypobasal. It need therefore be no cause for surprise, but rather of 

 increased interest that the point of origin of the first root should fluctuate 

 within the genus Eijuisctuin. Its indefinite position in different cases 

 stamps upon it with special clearness the character of an accessory to 

 the shoot itself, which its late appearance in certain Lycopods seems 

 further to confirm. The whole embryo thus consists of a spindle-like axis 

 with continued apical growth ; its base is like that of Isoetes without any 

 suspensor. The leaves and roots appear as appendages upon this spindle- 

 like axis. 



Naturally, the embryogeny of the fossil Equisetales is not accessible 

 for comparison. 



From the account of the Equisetales given in the above pages, it is 

 possible to form some idea of a primitive general type for the phylum. 

 They were probably, from the first, organisms with a prominent axis, 

 while the leaves, of moderate size, were arranged in whorls, with 

 elongated internodes between them. The root was an accessory addition 

 to the shoot. Spore-production, which is so important an event in the 

 antithetic alternation, does not figure in the early stages of life in 

 any known Equisetal type, but appears only late in the individual life. 

 There is little direct evidence among the Equisetales of any deferring 

 of spore-production, by abortion of sporangia or of sporangiophores, com- 

 parable with that which is so clearly indicated in the Lycopodiales. But 

 comparative evidence shows that in the Equisetales spore-production is not 

 restricted to branches of any definite rank, and transfers of the reproduc- 

 tive function from branches of one rank to those of a higher rank may 

 occur in nature, and are illustrated in various living species of Equisetiim. 

 This, coupled with the fact that there is essential structural similarity 

 between axes of all ranks in these plants, makes it seem probable that 

 axes of lower rank, and finally even the primary axis itself, may have 

 been fertile in a primitive Equisetoid type : that a deferring of spore- 

 production by transfer from axes of lower to those of higher order 

 occurred, and that thus the initial vegetative system was greatly extended. 

 In the Calamarians a secondary development of tissues in the axis accom- 

 panies the enlargement of the vegetative system, which thus attained 

 dendroid characters, now only faintly reflected in the smaller living forms. 



It would appear from the elongated form of the lax cone in such types 

 as Calamostachys, and especially from the usual intermixture of bract-leaves 

 and sporangiophores in them, that among early Equisetal types a condition 

 existed not unlike that of the undifferentiated Lycopod shoot of the Sela^o 

 type : that is, a general-purposes shoot, in which the office of spore- 

 production was not strictly differentiated from the function of nutrition, 



