68 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



sketch about twice the natural size and label it x 2. Describe 

 the difference in appearance between the outer and the inner 

 surface of the sepal and of the petal. N'ote the little scale 

 at the base of the petal, inside. Lift up the free edge of this 

 scale with the point of a needle and look for nectar. 



D. Strip off all the parts from a flower which has lost its 

 petals, until nothing is left but a slender, conical object a 

 little more than an eighth of an inch in length. This is 

 the receptacle or summit of the flower stalk. 



E. In a fully opened flower note the numerous yellow-tipped 

 stamens, each consisting of a short stalk, the filament, and 

 an enlarged yellow knob at the end, the anther. Note the 

 division of the anther into two portions, which appear from 

 the outside as parallel ridges, but which are really closed 

 cavities full of pollen. 



F. Observe in the interior of the flower the somewhat globular 

 mass (in a young flower almost covered by the stamens). 

 This is a group of pistils. Study one of these groups in a 

 flower from which the stamens have mostly fallen off, and 

 make an enlarged sketch of the head of pistils. Eemove 

 some of the pistils from a mature head, and sketch a single 

 one as seen with the magnifying glass. Label the little 

 knob or beak at the upper end of the pistil stigma, and the 

 main body of the pistil the ovary. Make a section of one of 

 the pistils, parallel to the flattened surfaces, and note the 

 partially matured seed within. 



POLLINATION AND FERTILIZATION 

 EXPERIMENT XLII 



Production of pollen tubes.* * Make a hanging-drop culture 

 (Sec. 204), or place a few drops of suitably diluted sirup of cane 

 sui>ar (Sec. 170), with some fresh pollen, in a concave cell ground 

 in a microscope slide, and cover with a thin glass circle. Place 

 the slide under a bell glass, with a wet cloth or sponge, to prevent 



