240 Introduction to Botany. 



to point directly upward or downward ? (We want to find 

 out by this question whether the pose of the flower is cor- 

 related with its form and construction.) Draw the dif- 

 ferent parts of a flower. Make cross and longitudinal 

 diagrams of a flower. (A suggested method of treatment 

 in diagraming a violet is given on page 154, but the 

 student should make each diagram accurately show the 

 characteristics of the species in hand.) Note that the pis- 

 til of the violet is one-celled but compound, as shown by 

 the three placentae. Study the inconspicuous cleistoga- 

 mous flowers that appear later on short peduncles. Show 

 how self pollination is accomplished in these flowers. Do 

 the early and conspicuous or later cleistogamous flowers 

 appear to be the more fruitful .? It seems from a study of 

 the violet that the cleistogamous flowers are remarkably 

 successful in accomplishing self fertiHzation ; the evil 

 results which might be expected to follow are apparently 

 kept from accumulating in the species by the occurrence 

 of cross fertilization in the early, conspicuous flowers. 



Write a short essay on the genus Viola, covering habitat, 

 time of blooming, form of plant, forms of leaves, coloration 

 of flowers, variations in details of floral structure in the 

 different species, relative fertility of conspicuous and 

 cleistogamous flowers, aesthetic considerations. 

 ' Let the student test his thoroughness and accuracy by 

 comparing the results of his work with the following inter- 

 esting account by Sprengel of his own discoveries relating 

 to the violet : — 



" The nectar receptacle is the end of the spur of the 

 corolla. At first I could not understand why in Viola 

 canina I should find nectar there but not on the nectary ; 

 but finally I perceived that this occurs naturally, for the 

 end of the spur has the form of an arch which curves 



