202 PRACTICAL BOTANY 



glycerine : in pollen-grains so prepared the two nuclei may be 

 found to be stained : better results may be obtained by careful 

 staining with hsematoxylin. 



B. Mount in half glycerine, half alcohol, some almost 

 mature pollen of Fritillaria imperialis, which has 

 been previously preserved in alcohol, and examine with 

 a high power. The grains have a smooth wall, and in 

 the granular protoplasm may usually be seen two 

 nuclei. If the grains be stained with haBmatoxylin 

 before mounting in glycerine and alcohol, the nuclei will 

 be more easily made out. 



Mount and examine, as types of the various forms of the grains, 

 the pollen of Selianthus, Althcea, Cucurlita, (Enothera, Orchis 

 (pollen-masses or pollinia), Mimosa, Cichor'mm, Rhododendron, or 

 Azalea, &c. 



C. In order to observe the germination of the pollen- 

 grains, and formation of the pollen-tubes, cultures may be 

 made in a watch glass, or, if it is desired to follow the 

 process in single individual grains, use may be made of 

 the moist chamber described in Appendix A. 



Mount some pollen-grains of HeliantTius or of Lilium 

 in one hanging drop of a weak solution of cane-sugar 

 in water (about 5 per cent.). Examine them with a 

 high power, and note their form and the external 

 configuration of their walls. 



Keep them at an ordinary temperature in the dark 

 for 12 to 18 hours : on again examining them, many will 

 be found to have put out pollen-tubes,, filled with 

 granular protoplasm, in which, after suitable staining, 

 two or more nuclei may be detected. 



