Zea mays:  Sensitiveness of the apex of the Radicle to contact.—­A large number of trials were made on this plant, as it was the only monocotyledon on which we experimented.  An abstract of the results will suffice.  In the first place, 22 germinating seeds were pinned to cork-lids without any object being attached to their radicles, some being exposed to a temperature of 65o — 66o F., and others to between 74o and 79o; and none of them became curved, though some were a little inclined to one side.  A few were selected, which from having germinated on sand were crooked, but when suspended in damp air the terminal part grew straight downwards.  This fact having been ascertained, little squares of the card-like paper were affixed with shellac, on several occasions, to the tips of 68 radicles.  Of these the terminal growing part of 39 became within 24 h. conspicuously curved away from the attached squares and from the perpendicular; 13 out of the 39 forming hooks with their points directed towards the zenith, and 8 forming loops.  Moreover, 7 other radicles out of the 68, were slightly and two doubtfully deflected from the cards.  There remain 20 which were not affected; but 10 of these ought not to be counted; for one was diseased, two had their tips quite surrounded by shellac, and the squares on 7 had slipped so as to stand parallel to the apex, instead of obliquely [page 178] on it.  There were therefore only 10 out of the 68 which certainly were not acted on.  Some of the radicles which were experimented on were young and short, most of them of moderate length, and two or three exceeded three inches in length.  The curvature in the above cases occurred within 24 h., but it was often conspicuous within a much shorter period.  For instance, the terminal growing part of one radicle was bent upwards into a rectangle in 8 h. 15 m., and of another in 9 h.  On one occasion a hook was formed in 9 h.  Six of the radicles in a jar containing nine seeds, which stood on a sand-bath, raised to a temperature varying from 76o to 82o F., became hooked, and a seventh formed a complete loop, when first looked at after 15 hours.

The accompanying figures of four germinating seeds (Fig. 69) show, firstly, a radicle (A) the apex of which has become so much bent away from the attached square as to form a hook.  Secondly (B), a hook converted through the continued irritation of the card, aided perhaps by geotropism, into an almost complete circle or loop.  The tip in the act of forming a loop generally rubs against the upper part of the radicle, and pushes off the attached square; the loop then contracts or closes, but never disappears; and the apex afterwards grows vertically downwards, being no longer irritated by any attached object.  This frequently occurred, and is represented at C. The jar above mentioned with the six hooked radicles and another jar were kept for two additional days, for the sake of observing how the hooks would be modified.  Most of them became converted into simple loops, like