150 Sensitive Fern 
section and primary segments as are not lobed already become 
lobed, and contraction of the blade and recession of its margin 
are begun and carried far enough to produce the following results. 
The outermost part of the blade, containing most of the veins, 
disappears; a few free veinlets, remnants of the innermost 
areola, are left next the lobes’ midveins; the lobes are dis- 
connected, narrowed, shortened, and recurved until subglobose, 
finally splitting into segments and becoming soriferous; and 
the contraction eventually draws the blade’s primary segments, 
now pinne, backward and upward, and reflexes the subglobose 
soriferous lobes, now pinnules. Indusia occur on the transi- 
tional leaves as well as on the sporophylls. 
The transitional leaves constitute the so-called ‘‘var. obtusi- 
lobata” Torrey. Asthey represent merely the transition from 
the usual sterile leaf to the fully fledged sporophyll, it is scarcely 
necessary to say that to give them a distinctive name is absurd. 
The affinity of this plant with Lorinseria areolata is marked. 
Both plants are essentially akin in habit, have scattered leaves 
rising from a creeping rootstock, sterile leaves similar in char- 
acter and texture, and venation of the same type. 
As already stated, in O. sensibilis development of the blade’s 
two basal primary segments is peculiarly rapid, while in L. 
areolata contraction overtakes the corresponding part of the 
blade at an early stage of the leaf’s development.* This gives 
different aspects to the early leaves of the two plants, but by 
comparing the accounts of the development of their leaves it will 
be seen that development, while carried further in O. sensibilis 
than in L. areolata, is along similar lines in both. 
The transformation of the sterile leaf into a sporophyll is in 
* See page 125. 
