192 STUDY OF COMMON PLANTS. 



fruits. How many carpels • are there ? Attachment, 

 direction, and form of ovules? Mode of dehiscence? 

 How is the fruit to be classified ? 



III. Construct a diagram of the flower. 



IV. Compare the views of different writers regarding 

 the morphology of the flower of Cruciferse.^ 



RELATIONSHIP. 



I. Compare with shepherd's-purse such of the species 

 named above as can be procured, and determine what 

 characters they exhibit in common. Do they all have a 

 pungent juice ? Are they all herbaceous ? Are the flowers 

 on the same plan ? How far do the fruits and seeds agree 



in structure ? 



t 



II. Summarize the results of your observations in a 

 brief general description of cruciferous plants. 



Note. — To complete this comparative study at all satisfactorily will re- 

 quire much time and patience. In studying the seeds it will be best to 

 obtain those of different genera from the seed store, sow a part of them 

 in moist sawdust, and dissect carefully from day to day. If the time is 

 short, it may be best to limit the comparison to a very few species, but 

 if even two or three genera are thoroughly studied, and the descriptions 

 accompanied by floral diagrams and sketches of the structure of fruits 

 and seeds, the student cannot fail to be impressed, as in no other way, 

 with the persistent and marked features of this remarkable group of 

 plants. 



The flowers of the Cruciferae, notwithstanding their 

 great uniformity of structure, exhibit striking physiologi- 

 cal differences. The number and position of the nectaries 

 is extremely variable. Some have a strong odor, and in at 

 least one species this is associated with evening expansion 



1 Cf. Gray, Structural Botany, pp. 206, 207 ; Arthur, Barnes, and 

 Coulter, Plant Dissection, p. 238 (references in footnote). 



