234 M. Marc Micheli on some Recent 



possible, and that the intervention of insects is always ne- 

 cessary. 



In a multitude of cases the expansion of the stigma does not 

 take place at the same time as the opening of the stamens ; the 

 flowers are what are called " dichogamous," and may be pro- 

 tandric or protogynic. 



The former are most frequent. Entire and most important 

 families enter this category, such as the LabiatfB, the Scrophu- 

 lariacege, the Composite, and the Campanulacese. Here the 

 office of insects is very evidently necessary; and it is facilitated 

 by the most varied details of organization. For example, in 

 the whole of the immense group Compositfe* the five stamens 

 have the anthers soldered into a cylinder, which envelopes the 

 pistil ; they open and allow the pollen to escape before the 

 style has become elongated. The style bears, below the 

 stigma, a certain number of rigid hairs, which retain the pollen- 

 grains, and carry them forward with them in their ascending 

 movement at the moment of the elongation of the style. The 

 pollen thus carried up out of the cylinder of the anthers is col- 

 lected by insects and transported to flowers the stigma of which 

 is already expanded. 



In the Campanulaceasf, Lobeliaceaj, &c. the system is the 

 same, only the appendages destined to retain the pollen on the 

 style present a very variable form. 



In the whole of the group of Scrophulariaceous Labiatse % the 

 axis of the flower is horizontal, and the stamens are approxi- 

 mated beneath the upper lip of the corolla. The insects, in 

 passing, separate and jostle them, cause the pollen to fall from 

 them, and then transport it to a more advanced flower. In 

 certain genera the stamens alone stand in the way of the insect, 

 which always seeks the bottom of the flower, where the nectaries 

 are. Later on they curve outwards, the style in its turn becomes 

 elongated, and advances to take their place, and its recurved 

 extremity caresses the body of the insect loaded with pollen. 



In certain plants in which the expansion of the reproductive 

 organs is simultaneous, the part performed by insects is no less 

 maintained. In their absence spontaneous fecundation, which 

 nevertheless appears to be inevitable, does not take place, or 

 produces very little effect. Such, for example, are numerous 

 Leguminosse §, in which the stamens and the pistil are enclosed 

 in the keel, in very close proximity. Insects, going to collect 



* " Ueber die Gesclileclitsverlialtiiisse bei den Compositen," Acta Leop. 

 Carol. Tol. XXV. 1869, and Bot. Zeitung, 1870, No. 30. 



t "Ulteriori osservazioni suUa dicogamia nel regno vegetale," Atti 

 della Soc. Ital. di Sci. Nat. vols. xi. & xii. ; and Bot. Zeitung, 1870, Nos. 

 37-42. X Ihid. § Ibid. 



