n8 PRACTICAL BOTANY 



of intercellular spaces between them, and the inner layer is not 

 spirally thickened : this is the line of dehiscence of the anther, 

 and the lax character of the tissue at this point helps to bring 

 about the rupture. 



3. The pollen-grains or microspores, which are almost 

 spherical, with smooth walls and granular protoplasmic con- 

 tents, 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 pre- 

 served 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 one of which occupies a lateral position, and 

 is surrounded by a definite body of protoplasm. If the grains 

 be stained with hasmatoxylin before mounting in glycerine and 

 alcohol, the nuclei will be more easily made out. Pollen of 

 Iris pseudacorus will also give satisfactory results : it may be 

 treated as above or stained in fresh condition with methyl green 

 and acetic acid : wash in weak acetic acid, and mount in the 

 same, or in very weak glycerine. 



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 Helianthns or of Lilitim 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 

 1 8 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. 



If transverse sections be made from very young buds of 

 Caltha, and successfully from older ones up to the mature 

 flower, the development of the anther and of the pollen may be 

 traced. 



The material should be preserved in absolute alcohol (or strong 



