Here is a more interesting case:  seedlings of Cassia tora in two pots, which had stood for some time on the table in the room just described, had their cotyledons horizontal.  One pot was now exposed for 2 h. to dull sunshine, and the cotyledons [page 125] remained horizontal; it was then brought back to the table, and after 50 m. the cotyledons had risen 68o above the horizon.  The other pot was placed during the same 2 h. behind a screen in the room, where the light was very obscure, and the cotyledons rose 63o above the horizon; the pot was then replaced on the table, and after 50 m. the cotyledons had fallen 33o.  These two pots with seedlings of the same age stood close together, and were exposed to exactly the same amount of light, yet the cotyledons in the one pot were rising, whilst those in the other pot were at the same time sinking.  This fact illustrates in a striking manner that their movements are not governed by the actual amount, but by a change in the intensity or degree of the light.  A similar experiment was tried with two sets of seedlings, both exposed to a dull light, but different in degree, and the result was the same.  The movements of the cotyledons of this Cassia are, however, determined (as in many other cases) largely by habit or inheritance, independently of light; for seedlings which had been moderately illuminated during the day, were kept all night and on the following morning in complete darkness; yet the cotyledons were partially open in the morning and remained open in the dark for about 6 h.  The cotyledons in another pot, similarly treated on another occasion, were open at 7 A.M. and remained open in the dark for 4 h. 30 m., after which time they began to close.  Yet these same seedlings, when brought in the middle of the day from a moderately bright into only a moderately dull light raised, as we have seen, their cotyledons high above the horizon.

Sensitiveness of Cotyledons to contact.—­This subject does not possess much interest, as it is not known that sensitiveness of this kind is of any service to seedling plants.  We have observed cases in only four genera, though we have vainly observed the cotyledons of many others.  The genus cassia seems to be pre-eminent in this respect:  thus, the cotyledons of C. tora, when extended horizontally, were both lightly tapped with a very thin twig for 3 m. and in the course of a few minutes they formed together an angle of 90o, so that each had risen 45o.  A single cotyledon of another seedling was tapped in a like manner for 1 m., and it rose 27o in 9 m.; and after eight additional minutes it had risen 10o more; the opposite cotyledon, which was not tapped, hardly moved at all.  The cotyledons in all these cases became horizontal again in less than half an hour.  The pulvinus is the most sensitive part, for on slightly pricking three cotyledons with a [page 126] pin in this part, they rose up vertically; but the blade was found also to be sensitive, care