236 BOTANT. 



togamy). There are a good many plants, however, which 

 have two forms of flowers, viz., larg^e, showy, nectar-bear- 

 ing, insect-pollinated ones, and small, inconspicuous self- 

 pollinated ones, generally with a rudimentary perianth. 

 -Flowers exhibiting this form of autogamy are said to be 

 cleistogamous. 



503. Examples are to be met with in some violets, wild 

 touch-me-not, etc.: early in the season these have large 

 flowers, which are pollinated by insects, but later only small 

 cleistogamous ones appear, and in some violets these are 

 subterranean. Without doubt it frequently happens that 

 the pollen of wind- and insectrpoUinated flowers falls upon 

 their stigmas, resulting in accidental self-pollination; but 

 too frequent a recurrence of this is guarded against by 

 various structural devices. 



504. The foregoing are but a few of the general modifi- 

 cations for securing proper pollination which flowers show; 

 they must serve to direct the student's attention to this 

 interesting part of the study of plants, which can be taken 

 up in connection with the writings of Darwin, Miiller, 

 Gray, and others. 



Practical Studies. — («) Collect a few wild buttercup flowers. Begin 

 at tlie lower side of the flower and carefully remove the flve green 

 sepals constituting the so-called calj'x, next the five yellow petals 

 constituting the so-called corolla, next the many stamens, and last 

 the numerous small pistils which cover the rounded end of the floral 

 stem. Make a caieful drawing of a representative of each part. 



(ft) Mount in water (.'ifter moistening with alcohol) a little of the 

 pollen of the morning-glory, sunflower, mallow, and Indian corn. 

 Note the surface markings. Crush the cells and test with iodine. 

 Pollen-grains may he germinated by placing them in a five-per-cent 

 solution of common sugar in water. The pollen-tubes may also be 

 found by carefully mounting stiirmas or longitudinal sections of stig- 

 mas. Many grasses are good subjects for such studies. 



(c) Remove the pistil from a fresh pea-flower. Split it longitudi- 

 nally, and observe that th? ovules are in a row along one seam (suture). 



