OXALIS. 91 



of Geranium, are 5-parted throughout ; sepals 5, petals 5, 

 stamens 2x5, and pistils 5, with their styles distinct and 

 their ovaries united (6). The stamens are also united at 

 the base, or monadelphous (monos, one, adelphos, brother- 

 hood), (3). 



^&$tivation. Here recurs an interesting topic sug- 

 gested by the curious posture of the petals when just open- 

 ing. How are they folded together in the bud ? The in- 

 quiry is important, since many genera and even some orders 

 are characterized by their mode of aestivation. (See the 

 plan, 1.) In reference to the Wood Sorrel the student 

 would instantly reply, " The petals are twisted in the bud I" 

 And the terms contorted or convolute express the idea. The 

 petals are all rolled together in one direction, each having 

 one edge within and one without. The same is true of the 

 flowers of Cranebills, and generally of Storkbills. 



Sleep. At the approach of night, or in cloudy weather, 

 these flowers close up and foid their contorted petals again 

 as in the bud. So also do the leaves. At night each leaflet 

 falls back on the stalk, folds its two halves together face to 

 face, and thus remains asleep, as it were, until awakened by 

 the morning sun.* 



* The vigils of plants are evidently dependent on the degree of light ; but different 

 species are variously affected. While many, like Oxalis, open and close with the day 

 for many days in succession, others, like the Morning Glory or the Portulacas, open 

 for a day only, and perish. The evening Primrose opens at 6 o'clock P. M. for a 

 night, perishing at sunrise ; and the Four-o-clock at about that hour for a few hours 

 only, and the Water Lily CNymphsea) opens and reopens only while the sun is high, 

 from 8 to 2. And there are other plants which, like the Gerania, open once for all, 

 and close not by night or day, until they close forever. 



Recent researches show that the sleep of plants generally bears some relation to 

 their peculiar wants. Thus the Daisy closes its flowers and hangs its head when 

 night comes on, or the gathering clouds forbode a storm, lest the dew or rain dissolve 

 the nectar stored up in its florets. The Nipplewort. (Lapsana), common in Europe, 

 opens before six and closes before ten in the morning, in order that the bees who are 

 early risers may taste its nectar, and not the ants, who delay until the dew is off, and 

 would not scatter its pollen. Again, night-flowers are adapted to the habits of certain 

 nocturnal moths which are needful agents in their fertilization. Such flowers are 

 always white or pale yellow, the only colors visible in the darkness. 



