It is a very general rule that the first true leaf, though it may differ
Notwithstanding what has just been said, it may be strongly suspected that in some cases the rising of the petioles, when considerable, does beneficially serve the plant by greatly reducing the surface exposed to radiation at night. Ifthe reader will compare the two drawings (Fig. 155, p. 277) of Cassia pubescens, copied from photographs, he will see that ihe diameter of the plant at night is about one-third of what it is by day, and therefore the surface exposed to radiation is nearly nine times less. A similar conclusion may be deduced from the drawings (Fig. 149, p. 266) of a branch awake and asleep of Desmodium gyrans. So it was in a very striking manner with young plants of Bauhinia, and with Oxalis Ortegesii.