Elementary botany . rmediate conditions of the sterileand the fertile leaf. A number of years ago it was thought bysome that this represented a different species, but now it is known V 4& ? 1 /^*V Fig. fern, showing one vegetative leaf and two sporophylls completely transformed. that these intermediate forms are partly transformed fertile is a very easy matter in the case of the sensitive fern to pro-duce these transformations by experiment. If one in the spring,when the sterile leaves attain a height of 12 to 16 cm (8-10inches), cuts them away, and again when they have
Elementary botany . rmediate conditions of the sterileand the fertile leaf. A number of years ago it was thought bysome that this represented a different species, but now it is known V 4& ? 1 /^*V Fig. fern, showing one vegetative leaf and two sporophylls completely transformed. that these intermediate forms are partly transformed fertile is a very easy matter in the case of the sensitive fern to pro-duce these transformations by experiment. If one in the spring,when the sterile leaves attain a height of 12 to 16 cm (8-10inches), cuts them away, and again when they have a secondtime reached the same height, some of the fruiting leaves whichdevelop later will be transformed. A few years ago I cut off the DIMORPHISM OF FERNS. 277 sterile leaves from quite a large patch of the sensitive fern, oncein May, and again in June. In July, when the fertile leaveswere appearing above the ground, many of them were changedpartly or completely into sterile leaves. In all some thirty plants. Fig. and transformed sporophyll of sensitive fern. showed these transformations, so that every conceivable gradationwas obtained between the two kinds of leaves. 567. It is quite interesting to note the form of these changedleaves carefully, to see how this change has affected the pinnaeand the sporangia. We note that the tip of the leaf as well ast\\e tips of all the pinnae are more expanded than the basal por- 278 MORPHOL OGY. tions of the same. This is due to the fact that the tip of theleaf develops later than the basal portions. At the time thestimulus to the change in the development of the fertile leavesreached them they were partly formed, that is the basal parts ofthe fertile leaves were more or less developed and fixed andcould not change. Those portions of the leaf, however, whichwere not yet completely formed, under this stimulus, or throughcorrelation of growth, are incited to vegetative growth, and ex-pand more or less completely into vegetative
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