THE STAMEN. 127 



3. Pollen-grains or Microspores are almost sphe- 

 rical, with smooth walls, and granular protoplasmic 

 contents, in which may be made out, with difficulty, 

 two nuclei. 



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. N.B. If the grains be stained with hsematoxy- 

 lin 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 HeliantTius, Althcea, Cucurbita, 

 CEnothera, Orchis (pollen-masses or pollinia), Mimosa, 

 Cichorium, &c. 



C. In order to observe the germination of the 

 pollen-grains, and formation of the pollen-tubes, use 

 may be made of the moist chamber, described on 

 p. 16. 



Mount some pollen-grains of HeliantJius 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 a few hours : on again examining them, many will 

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

 granular protoplasm, in which one or more nuclei 

 might be detected. 



The same method may be used for the pollen of other plants, 

 e.g. Orchids, species of Tulipa, Fritillaria, Nymphcea, &c. It 



