CHAP. VI. SLEEP OF COTYLEDONS. 303 



Although the movement of the cotyledons endured for a long 

 time, no pulvinus was exteriorly visible; but their growth 

 continued for a long time. The cotyledons appear to be only 

 slightly heliotropic, though the hypocotyl is strongly so. 



Gossypium arboreum (?) (var. Nankin cotton) (Malvaceae). The 

 cotyledons behave in nearly the same manner as those of the 

 Anoda. On June 15th the cotyledons of two seedlings were 

 65 inch in length (measured along the midrib) and stood hori- 

 zontally at noon ; at 10 P.M. they occupied the same position 

 and had not fallen at all. On June 23rd, the cotyledons of one 

 of these seedlings were I'l inch in length, and by 10 P.M. they 

 had fallen from a horizontal position to 62 beneath the horizon. 

 The cotyledons of the other seedling were 1*3 inch in length, and 

 a minute true leaf had been formed ; they had fallen at 10 P.M. 

 to 70 beneath the horizon. On June 25th, the true leaf of this 

 latter seedling was '9 inch in length, and the cotyledons occu- 

 pied nearly the same position at night. By July 9th the cotyle- 

 dons appeared very old and showed signs of withering; but they 

 stood at noon almost horizontally, and at 10 P.M. hung down 

 vertically. 



Oossypium herbaceum. It is remarkable that the cotyledons of 

 this species behave differently from those of the last. They were 

 observed during 6 weeks from their first development until 

 they had grown to a very large size (still appearing fresh and 

 green), viz. 2 inches in breadth. At this age a true leaf had 

 been formed, which with its petiole was 2 inches long. During 

 the whole of these 6 weeks the cotyledons did not sink at night ; 

 yet when old their weight was considerable and they were borne 

 by much elongated petioles. Seedlings raised from some seed 

 sent us from Naples, behaved in the same manner ; as did those 

 of a kind cultivated in Alabama and of the Sea-island cotton. 

 To what species these three latter forms belong we do not know. 

 We could not make out in the case of the Naples cotton, that 

 the position of the cotyledons at night was influenced by the 

 soil being more or less dry ; care being taken that they were 

 not rendered flaccid by being too dry. The weight of the large 

 cotyledons of the Alabama and Sea-island kinds caused them to 

 hang somewhat downwards, when the pots in which they grew 

 were left for a time upside down. It should, however, be 

 observed that these three kinds were raised in the middle of 

 the winter, which sometimes greatly interferes with the proper 

 nyctitropic movements of leaves and cotyledons. 

 14 



