MORPHOLOGY OF ANGIOSPERMS. 135 



strawberry flowers the petals become green and leaf-like, and the 

 change is spoken of as chlorosis or chloranthy. In some 

 flowers even the ovules are replaced by leaf-like processes or 

 appendages, as in Drosera and clover. 



Arrested Development. — The arrest or suppression of 

 parts of the plant, particularly of the flower, is of very common 

 occurrence. Just as there are millions of seeds that never find 

 suitable conditions for germination, so in the flowers of a large 

 number of plants a very large proportion of the ovules never 

 develop into seeds, the plants in many instances not furnishing 

 sufficient nutriment for all of the ovules to mature. Under leaves 

 it was stated that in the axil of each leaf there is a bud. This is 

 not always apparent, but if the plant be subjected to some special 

 stimulus, some of the latent buds will become evident. For 

 example, the rubber plant (Ficus), so commonly cultivated as an 

 ornamental plant, shows a tendency to develop a straight, un- 

 branched shoot, but if the tip of the shoot be cut ofif, the buds in 

 the axils of the upper leaves will develop into branches, while 

 some of those lower down will form small protuberances, but 

 develop no further. In other cases there is a loss of parts which 

 seems to be due to loss of function. When there is a partial loss 

 of the element, as of the anthers in the flower of catalpa, it is 

 said to be imperfectly developed or abortive. When the entire ele- 

 ment remains undeveloped as in some of the stamens of the Labi- 

 atae, it is said to be suppressed (Fig. 84, F). In flax the stamens of 

 the outer whorl are reduced to thread-like processes. Such sterile 

 or aborted stamens are called staminodes (staminodia). In other 

 plants the parts are not apparently arrested, but have not yet been 

 differentiated, as is the case in the Lily family where the perianth 

 is composed of segments which are more or less alike (Fig. 123). 

 In other cases, however, there seems to be a suppression or arrest 

 of the floral envelopes. 



Cleistogatnous Flowers. — In addition to the regular 

 flowers some plants produce cleistogamous or closed flowers. In 

 these flowers the corolla is usually suppressed. The flowers 

 develop stamens and pistils but remain closed, and thus there is 

 no chance for cross-pollination. The cleistogamous flowers appear 

 later than the regular flowers and are more or less inconspicuous. 



