294 EXPERIMENTS WITH PLANTS 



tubes; and we suppose that the tubes are attracted to 

 the ovules in the same way. 



The fact that pollen -grains germinate or burst 

 when placed in water shows the importance of protect- 

 ing them from rain and dew, since they are not, when 

 germinating, in suitable condition for transportation 

 (any more than germinating seeds would be) . l Notice 

 how quickly they dry up and perish if exposed to dry 

 air while in this condition. 



Do you find devices to protect the pollen from rain ? 

 Examine as many kinds of flowers as you can after a 

 shower, or sprinkle them with a watering-pot and note 

 the result. Here we find so many different ways of 

 solving the same problem that it is an interesting 

 matter to study. The flowers may be protected by the 

 leaves (Jewelweed, Linden), by the sepals (Acanthus), 

 by the closed petals (Pea family, Snapdragon), by 

 an arching roof (Violet, Monkshood), by contract- 

 ing the tube of the corolla above the stamens (Phlox, 

 Primrose) or by the stigma (Iris). 2 



Many flowers grow in a horizontal position or hang 

 downward, which effectually prevents the entrance of 

 rain. Others, which grow upright, assume a droop- 



1 The pollen, like the seed, varies greatly in the length of time it retains its 

 vitality. Ordinarily it will keep for at least a week in a cool, dry place, without 

 deterioration. The Arabs, who gather the pollen of the Date Palm for arti- 

 ficial pollination, appear to keep it for one or even two years without much 

 loss of vitality. See an article by Swingle on the Date Palm in the Year Book 

 of the U. S. Dept. of Agriculture for 1900. 



2 See Kerner and Oliver, "Natural History of Plants," Vol. II, p. 104. 



