FERTILIZATION. 47 



& 47), forming the rudimentary embryo ; and from 

 this, by further growth, the perfected embryo (fig. 55) 

 results ; or, to use a fashionable technical term, the 

 simply cellular embryonic mass becomes differen- 

 tiated into the radicle, cotyledons, and plumule, form- 

 ing the embryo. It will be remarked that the posi- 

 tion of the embryo in fig. 55 is the reverse of that in 

 figs. 46 & 47, the radicle in the former being directed 

 downwards, whilst that of the embryo in the figure of 

 the embryo-sac (fig. 47) is directed upwards. 



The embryonal structures are very difficult of de- 

 tection ; but it happens that in our little chickweed 

 they are more easily dissected out than in most other 

 plants. For this purpose, the ovules, placed on a 

 slide and lying in water, should be picked to pieces 

 with the mounted needles, under the simple micro- 

 scope. They may be preserved in chloride of calcium 

 or glycerine. 



A clear distinction must be drawn between seeds, 

 which result from the process of fertilization, and 

 buds, which are formed independently of this process. 

 Both consist essentially of embryo plants ; but while 

 the former originate from a single cell, the latter are 

 outgrowths of a parent stem, from which their tissues 

 are derived ; and while the former propagate the spe- 

 cies, the latter increase the individual. 



The obvious use of seeds is the distribution of the 

 species by the formation of new individuals. 



In the general outline which has been given of the 

 elements, tissues, and organs of plants, they have 

 been examined principally as existing in the higher 

 groups, or those of more complex structure ; and to 

 enter further upon a description of these plants would 

 involve the consideration of variations in the form 

 and arrangement of the organs of which they are 

 composed. As these can mostly be investigated with- 

 out the use of the microscope, we must pass to those 

 in which the entire plant consists of little more than 



