MORPHOLOGY OF HIGHER PLANTS. 391 



{Nymphcca) there is a series of parts ranging from stamens with 

 narrow filaments and stamens with broad petaloid filaments to 

 petals tipped with a small anther and regular petals (Fig. 221, A). 

 In this case the stamens are considered to result from the trans- 

 formation of the petals. In the case of green roses and green 

 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 occur- 

 rence. 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 cjltivated as an 

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

 branched shoot, but if the tip of the shoot be cut off, 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- 

 atse, it is said to be suppressed (Fig. 223, F). In flax the stamens 

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

 sterile or aborted stamens are called stamixodes (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. 269). In other cases, however, there seems to be a suppres- 

 sion or arrest of the floral envelopes. 



Cleistogamous Flowers.— In addition to the. regular flowers 



