URTICACE^ 



357 



plasm in the stinging hairs. He found that it was 

 repelled by red light, and attracted by blue. No 

 doubt, however, the protoplasm would react differently 

 in different species. The filaments bearing the anthers 

 are coiled in the bud and suddenly spring up at the 

 moment the anthers open, thus ejecting the pollen in 

 little puffs. This happens on bright summer mornings 

 as soon as they are touched by the sun, and the 

 cannonade lasts about half an hour. 



Parietaria (Pellitory) 



There are three forms of flower — complete, male, and 

 female. Male flowers as in the Nettle. Female, with a 

 tubular or campanulate four-lobed perianth and a brush- 

 like stigma. The complete flowers are protogynous. 



P. oflBcinalis is the only British species. The stamens 

 explode as in Urtica. The name is 

 derived from the habit of the plant to 

 grow on old walls. The stem and 

 leaves are pubescent, with curled hairs. 



HuMULTJS (Hop) 



Dioecious wind flowers. A climber. 



H. Lupulus.- — The stigmas of the 

 female flowers are ripe at least two 

 days before the anthers of the male 

 plants open. The orifice of the anther 

 is small, so that the pollen is gradually 

 scattered. The stipules (Fig. 233) are 

 interesting : they are connate, but the 

 two which have joined belong to oppo- 

 site leaves. This explains the deep 

 notch at the end. The leaves are 

 smooth above and rough below. The 

 upper part of the shoot, as in other 

 climbers, revolves in a circle or ellipse, 

 the object being to find some support up which to 

 climb. The direction is always towards the right, 

 and on an average a revolution takes 2 hours and 



Fia. 233.— End of shoot 

 of Hop, showiEg 

 connate stipules in 

 pairs. 



