TRUE NATURE OF FLORAL ORGANS. 155 
charged and how it is carried from flower to flower. The 
commonest method is to have the anther-cells split length- 
wise, as in Fig. 138, I. A few anthers open by trap-doors 
like valves, as in II, and a larger number by little holes at 
the top, as in III. 
The pollen, in many plants with inconspicuous flowers, as 
the evergreen cone-bearing trees, the grasses, rushes, and 
sedges, is a fine, dry powder. In plants with showy flowers 
it is often somewhat sticky or pasty. The forms of pollen- 
grains are extremely various. That of the tulip (Fig. 116), 
and the kinds shown in Fig. 
139 will serve as examples of 
some of the shapes which the 
grains assume; IV in the latter 
figure is perhaps as common a 
form as any. Each pollen-grain 
consists mainly of a single cell, 
and is covered by a moderately 
thick outer wall and a thin inner 
one. Its contents is a thickish 
protoplasm, full of little opaque 
particles and usually containing 
erains of starch and little drops 
of oil. The larger knobs on the 
outer coat, as at k (Fig. 139, I Fig. 139, — Pollen-Grains. 
aad-t1), marktheispots at which, 1 hazel; I, coltefooh; IU, ike 
; 5 ; ginger; IV, hepatica; V, pine; 
the inner coat of the grain is $s, air-sacs, (All magnified 300 
finally to burst through the outer —_—iameters.) 
one, pushing its way out in the form of a slender, thin-walled 
tube.? 
190. Experiment 32. Production of Pollen Tubes. — Place a few 
drops of suitably diluted syrup? with some fresh pollen in a concave cell 
ground in a microscope slide; cover with thin glass circle ; place under 
1 See Kerner and Oliver, vol. II, pp. 95-104. 2 See Appendix B, 
