THE "SELAGO" CONDITION 



167 



incomplete parts where present as vestigial, and a similar conclusion seems 

 justified for the Ophioglossaceae. It may thus be held that in the mature 

 plant of the Ophioglossaceae all the leaves are potentially fertile : the 

 sterile foliage leaf is merely the part which remains when the spike is 

 abortive, and its genetic relation to the fully matured sporophyll is the 

 same as that of the sterile to the fertile leaf in Z. Selago or in Isoetes. 



There remains for consideration from this same point of view the large 

 series of the Ferns. Notwithstanding the preponderant size of their leaves, 

 and the wide distribution of the sori and sporangia over their large surface, 

 they should still be studied in the 

 same way as other Pteridophytes: their 

 difference of conformation should not 

 be allowed to affect the recognition of 

 such similarity in the relations of the 

 vegetative and propagative parts as may 

 ^xist between them and the smaller- 

 leaved forms. Since the relation of 

 leaf to axis is essentially the same in 

 Ferns as in other Vascular Plants, the 

 whole shoot may be held as equivalent 

 to the shoot, for instance, of an Isoetes; 

 and this aspect of it may be maintained 

 equally in those cases where the axis is 

 short and the leaves crowded upon it, 

 -and also in those where the axis is 

 elongated and the leaves isolated at 

 long intervals apart. Maintaining this 

 point of view of the shoot as a whole, 

 there is in the ontogeny of the Ferns 

 a preliminary vegetative phase, which 

 may be of varying extent ; subsequently 

 the fertile phase begins. The broad 

 relations of the two phases are thus 

 the same as in other Pteridophytes. 



The fertile region in Ferns is imperfectly differentiated, and it is in this 

 respect comparable with those imperfectly differentiated forms which show 

 what has been called the Selago condition. But the matter is further 

 complicated by the fact that in many Ferns the differentiation does not 

 involve whole leaves, but only parts of them ; the large Fern-leaf, in fact, 

 does not always behave as one unit, but the differentiation of sterile 

 and fertile regions may involve only parts of the individual leaf, not the 

 whole. 



Taking into consideration first the simpler case, where whole leaves 

 are differentiated either as sterile or fertile, examples are seen in such 

 cases as the common Hard Fern (Bkchnum boreale) or in the Ostrich 



FIG. 



Phyllotheca. Zigno. A , Ph. equisetiforinis 

 from Rovere di Velo, near Verona. Z>, inflores- 

 cence from Siberia, placed by Schmalhausen with 

 Phyllotheca. (After Solms.) 



