DICLINOUS FLO WEBS, CONCLUDED 169 



the central column shown at the left. It has two 

 parts. In the condition in which it is seen in 

 the picture, the lower part is developed, but the 

 upper part is not. Each of the numerous objects 

 on the lower part is found, upon being sectioned, 

 to contain three cavities, which contain ovules. 

 These objects, therefore, are pistils. If the same 

 calla were seen a few days later, the upper part 

 of the spike would be found to be in bloom, but 

 the flowers would comprise only stamens. In other 

 words, the central column in a calla is an androgy- 

 nous spike, comprising very many flowers. 



190o. A noticeable feature of this spike is the great difference 

 in time of maturity of the two kinds of flowers. The spike is 

 strongly dichogamous. In this case, the pistils mature first, whence 

 the plant is said to be proterogynous ("pistils earliest"), but in 

 many other plants the stamens mature first, plant proterandrous 

 ("stamens earliest"), although this condition is less frequent than 

 the other. 



191. The flowers of the calla, then, are naked 

 or achlamydeous (1526). The great white portion, 

 which we commonly call the "flower," is only a 

 reinforcement of the spike, the same as the four 

 great bracts reinforce the flower- head of the dog- 

 wood (Fig. 154). This particular kind of one-leaved 

 involucre is known as a spathe, and the spike 

 which is inclosed in it is a spadix. 



191a. The pupil should now examine the jaek-in-the- pulpit (or 

 Indian turnip), the skunk cabbage, and various spadiceous flowers 

 (like the anthuriums) of the greenhouses. Observe the great differ- 



