Negative heliotropism is much less frequent in plants. It has been observed in aërial roots, in many roots that are ordinarily buried in the ground, in anchoring tendrils that serve as holdfasts, and even in the stems of certain climbers. In all of these cases, and more especially in the case of the climbers, the reaction is obviously of advantage to the plant; and it is significant to find, in plants that climb by tendrils carrying adhering disks, that there is a reversal of the ordinary heliotropism shown by homologous organs in other plants. There is an obvious adaptation in the behavior of the tendril, since its growth away from the more illuminated side is just the sort of reaction that is likely to bring it into contact with a solid body. In this connection it is important to observe that these reactions to light are perfectly definite, being either positive or negative under given conditions, and therefore there is at present nothing to indicate that there has been a gradual transformation from positive to negative, or _vice versa_. It seems to me much more probable that when the structural change took place, that converted the plant into a climber, there appeared a new heliotropic response associated with the other change. In other words, both appeared together in the new organ, and neither was gradually acquired by picking out fluctuating variations. The leaves of plants also show a sort of transverse heliotropic response. It has been found, for example, that the leaves of Malva will turn completely over if illuminated by a mirror from below. A curious case of change of heliotropism is found in the flower stalks of Linaria. They are at first positively heliotropic, but after the flower has been fertilized the stalk becomes negatively heliotropic. As the stalks continue to grow longer, they push the fruits into the crevices of the rocks on which the plants grow, and in this way insure the lodgement of the seeds. Here we have an excellent example showing that the negative heliotropism of the flower stalk could scarcely have been acquired by slight changes in the final direction, for only the complete change is useful to the plant. Intermediate steps would have no special value. As has been pointed out in the case of the seedling plant, the main stem responds positively and the roots negatively to gravity. In addition to this, the lateral position taken by the lateral roots and branches and by underground stems are also, in part, due to a geotropic response. In this case also the effect is produced by the increased growth on the upper side when the response is positive, and on the lower when it is negative. Leaves also assume a transverse position in response to the action of gravity, or at least they make a definite angle with the direction of its action.