120 PLANT PHYSIOLOGY AND ECOLOGY 



or sculpturing of the pollen grain itself, or from the form of stamen^ 

 pistil, corolla, calyx, bract, or inflorescence. The thick wall of 

 the pollen grain is a very considerable protection, often increased 

 by oil or viscin, as in Onagra, Circcea, etc. Protection is also 

 brought about by the position of the anther, or through the location 

 of the pore by which the latter opens. In conifers the swelling 

 of the staminate scales when moist closes the way to the pollen 

 grains. Iris covers the stamen with a broad petaloid stigma. 

 Instances of protection by means of the shape of the corolla occur 

 abundantly among flowers with united petals, e.g., Androsace 

 Gentiana, Litliospermum, etc., and sometimes among those with 

 separate petals, such as Aconitum, Bicuculla, and Delphinium. 

 Certain cleistogamous, i.e., closed, flowers, also belong here. jNIore 

 rarely the calyx serves the same purpose, as in some species of 

 Clematis. In Arisoema and other AracecB, protection is brought 

 about by the form of the spathe. In certain catkin-bearers, 

 Populus especially, some shelter is afforded by the large bracts. 

 Protection as a result of the position of the flower or inflorescence 

 occurs in a large number of species in which the flowers are turned 

 toward the earth, and in flowers with tubular corollas which de- 

 viate even slightly from an upright position. To this class belong 

 Erythronium, Pentstemon, Teucrium, species of Gilia, etc. In 

 Tilia the flower clusters are placed in such a position that they 

 are sheltered by the leaves, a device which also occurs in some 

 species of Impatiens. 



143. Protection by movement. ^Mechanical devices comprise 

 movements of the flower or its parts, or of the flower cluster. The 

 movement is one of closing or of drooping. In most cases pro- 

 tection takes place by the closing of the corolla, more rarely by 

 the closing of other parts of the flower. This is especially w^ell 

 shown in day-bloomers and night-bloomers, particularly those 

 that are ephemeral, i.e., that wilt shortly after opening. Day- 

 blooming and night-blooming serve to protect the pollen during 

 the time when it is not being removed and may be injured, although 

 this habit was probably first acquired with relation to insect 

 visitors. The sepals sometimes close for protection in apetalous 

 forms. The swelling of scales in pine cones and the closing of 

 pores in some anthers should be mentioned here, though they are 

 not due to a definite movement. The protection which is obtained 

 in some flowers by a pendulous or ascending position is secured in 



