THE AMERICAN BOTANIST. 19 



lets to get the right amount of Hght. The midrib or rachis 

 is nearly erect, but the leaflets are often twisted until their 

 surfaces are parallel with the surface of the earth. 



Cleistogamous Flowers. — There seems to be a variety 

 of reasons for the occurrence of cleistogamous flowers. In 

 the violet family, variations in heat and cold seem to be the 

 main factors, and in the case of the oxalis, whose cleistogam- 

 ous flowers appear in summer, it has been conjectured that 

 the lack of proper insects to effect pollination is the cause. 

 In the early part of the year the insects visit the chasmogam- 

 ous, or open flowers of this plant, but later in the year are 

 attracted to other more showy flowers. The sundew affords 

 a still more remarkable cause. It is explained that the leaves 

 have become such expert insect-catchers, that the insects rarely 

 visit the flowers. This seems reasonable enough if applied 

 to the plants in some sections, but most of us know that the 

 sundew is not always cleistogamous. Other causes of cleis- 

 togamy in plants are lack of light, and inundation at the 

 blooming season. 



Function of Bud Scales. — The average person is in- 

 clined to imagine that the scales on the winter buds of trees 

 are for the purpose of keeping out the cold, but upon con- 

 sideration it is easy to see that this cannot be. In winter we 

 may find the buds frozen stiff. After a variety of experiments, 

 K. M. Wiegand concludes that the principal uses of bud-scales 

 are to protect the young leaves which they enfold from me- 

 chanical injury occasioned by the branches being whipped 

 about by the wind, and from the drying out of the moisture 

 they contain. This latter is doubtless the more important, for 

 even in the tropics where leaves are never exposed to cold, the 

 developing organs are often protected by stipules until they 

 can protect themselves. The hair and wool on the leaves of 

 plants are regarded as devices to prevent evaporation and it 



