THE NIGHTSHADE FAMILY. 221 



and Petunia. The last two are widely cultivated, and 

 their flowers may be had for weeks together. Attention 

 should be directed to 



1. Such general external features as the plants possess 



in common. Between certain species and genera 

 this likeness in general characters is very striking, 

 in other cases it is not apparent. 



2. Active properties, manifested in part by odor and 



taste. 



3. Structure of flower and fruit. 



4. Structure of seeds. The seeds of different plants of 



this family exhibit great likeness of form and 

 structure, as may be seen by comparing longitu- 

 dinal sections of those of tomato, egg-plant, 

 stramonium, etc. It is very desirable that the 

 student should make an extended and critical 

 comparison of the seeds of as many different 

 species as possible. This should be assigned as 

 a special study, and time given for a thorough 

 piece of work. 



II. Write a summary of the characters in which all the 

 species examined agree. 



III. Compare the characters of the Solanaceee with those 

 of any other families that you remember as showing resem- 

 blances to them. If you have already studied any of the 

 Scrophulariacese point out the best characters by which 

 the two families are to be distinguished. 



In the study of every family, comparisons of this kind 

 should be made as fast as the necessary data are in hand. 

 In most cases the relationships of families among them- 

 selves are by no means as satisfactorily made out as could 

 be desired, but that is no reason for not studying them. 



