The diminished size of the petals sometimes coexists with an increase in their number, as in a flower of Streptocarpus Rexii, mentioned by Bureau.[530]
Among monocotyledons this partial development seems to be even more frequent than in dicotyledons. In addition to the well-known cases of certain species of Bellevalia and Muscari, wherein the uppermost flowers of the raceme are more or less atrophied (see p. 347, fig. 179), a few less common illustrations may be cited. In crocuses it is not a very uncommon circumstance to find the three inner segments of the perianth smaller than natural, and generally unequal in size. This occurs without any other perceptible change in the flower.
Schlechtendal[531] mentions a flower of Fritillaria imperialis in which the perianthial leaves were relatively very small, and destitute of the usual nectary, while the stamens, on the other hand, were of their natural size and appearance. Fresenius[532] records a similar occurrence in the same plant.
Morren[533] gives details of like appearances in Hymenocallis americana, and Delavaud[534] in Tigridia pavonia.
In certain orchids an arrested development of the perianth is habitual, as in Oncidium abortivum (fig. 217), where, on a large branching panicle, numerous abortive, but few perfect, flowers are produced. In a similar way the petals and labellum of Odontoglossum Uro-Skinneri have been found reduced to filamentous processes.
Fig. 217.—Flower of Oncidium abortivum, magnified.
Abortion of the stamens.—Atrophy of one or more stamens is of very common occurrence, as a general rule, in many genera of plants, e.g. Scrophularia, Erodium, many Restiaceæ, &c. &c. As a strictly teratological condition atrophy of the stamens is more rare than complete suppression. It has been noticed in Arabis alpina, Cerastium glomeratum, C. tetrandrum, Rhamnus catharticus, Anemone, Hepatica, &c. It happens frequently among Orchids both wild and cultivated. In the Hymenocallis flowers described by the elder Morren, four out of five stamens were atrophied. In other flowers, otherwise perfectly formed, one abortive stamen was found bearing a spherical indehiscent anther. All these atrophied anthers of Hymenocallis were found to contain pollen, differing at first sight but little from what is usual, but presenting this important peculiarity, that while the normal pollen does not burst until it comes into contact with the stigma, in the abnormal flowers the outer coat of the pollen-grains split while still within the anther, from which latter, indeed, they could not escape, owing to the indehiscent nature of the latter. Again, the pollen-tube of the abnormal grains cracked, in its turn, on mere exposure to the air, and liberated the fovilla, so that the pollen of these atrophied anthers was necessarily impotent, because it opened before it could be applied to the stigma, even had that been rendered possible by the opening of the anther.