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. Sedago or in Lsoetes. 
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 
exist between them and the smaller- 
leaved forms. Since the relation of 
leaf to axis 1s 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 Lsoe/es ; 
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 pom Wovers di Velo, near Verna ioores 
relations of the two phases are thus i Sehmalhausen sith 
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 Seago 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 (Blechnum boreale) or in the Ostrich 
