110 BOTANY. 



stem, but at night they rise and are parallel to one another. 

 Seedlings of parsley, celery, tomato, and four-o'clock be- 

 have in a similar manner. In some cases the cotyledons, 

 instead of rising, at night, bend abruptly downwards. 

 This happens with seedlings of certain kinds of sorrel 

 (Oxalis), although curiously in other species of the same 

 genus the cotyledons rise. 



190. The leaves of many (if not all) plants assume a 

 position at night more or less difEerent from that which 

 they have during the day. In the common purslane the 

 leaves at night bend upwards in such a manner as to lie 

 more nearly parallel with the stem. In wood-sorrel 

 (Oxalis) the leaflets bend abruptly downward and closely 

 surround the common leaf-stalk. In clover, on the con- 

 trary, the leaflets bend upwards, afterwards folding over to 

 one side. In beans the leaflets sink down somewhat after 

 the manner of the wood-sorrel. In some cassias and the 

 sensitive-plants the nocturnal position differs remarkably 

 from that of the day ; not only are the leaflets folded, but 

 the leaf -stalks change their position, in some cases rising 

 and in others becoming sharply depressed. Even some 

 conifers have been observed to show a well-marked sleep- 

 ing state at night, and it is very likely that when we study 

 them attentively very few of the higher plants will be 

 found which are wanting in this power. The familiar 

 closing of certain flowers at night and opening again in the 

 morning, and the exactly reversed action, are to he re- 

 garded as of the same nature as the nyctitropic action of 



Practical Studies. — (a) Grow a nasturtium (Tropseolum) in a win- 

 dow, noting carefully tlie rapid bending of its leaves toward the 

 light. 



