290 



EXPERIMENTS WITH PLANTS 



grains. Fig. 162 shows the appearance of these in 



the Oat. 



Placed in a drop of water on a slide, covered 



with a cover -glass and examined under the high 

 power of the microscope, many of the 

 pollen -grains are seen to be sending 

 out long tubes (Fig. 163) which grow 

 down along the brush -like style to- 

 ward the ovary. What happens after 

 that can be seen only 



162. Ovary (seed-case) of in g d Sections, but 

 Oat with feathery style. ma y fa described HI a 



few words. Inside the ovary lies (as 

 you may see with a hand -lens) a tiny 

 seed or ovule (Fig. 161). Within this is 

 a mass of tissue, in the central cavity 

 (embryo sac, Fig. 164) of which lies the 

 egg. In the center of the egg is a 

 nucleus. The pollen -tube approaches 

 to within a short distance of the egg 

 and opens at the end ; a nucleus issues 

 from it which unites with the nucleus of 

 the egg, so that the two form a single 

 nucleus. The egg then begins to develop 

 and eventually forms a tiny plant, with 



T , , n -i . 



cauhcle and leaves, such as we find in 

 the ripened seed. 



Unless the union of the nuclei takes 



m s t y b i r e an S olt! 



showing a pol- 



ien-gram pushing 



out a long tube 



