334 AUTOGAMY. 



visit a flower, the anthers are still full of pollen at the close of its flowering period, 

 and being then displaced let fall their pollen upon the slightest vibration of the 

 pendent blossom, or even when it is quite still. The pollen falls straight down and 

 is caught by the stigma below. 



The process above described is only observed to take place in pendent flowers 

 where the pollen is of floury consistency and the stamens are united into a conical 

 cap. Flowers borne on horizontal stalks, and facing sideways, may exhibit the 

 same phenomenon in connection with separate stamens. Only an important 

 circumstance in this case is that some of the anthers should be exactly over the 

 stigmas at the time of dehiscence. With a view to cross-fertilization, lateral flowers 

 of the kind are protogynous, and have their anthers closed when the buds open; 

 but later on the anthers dehisce, and a portion of the pollen then liberated falls 

 out, owing to the contraction of the walls of the anthers, and besprinkles the 

 stigma of the same flower. This method of autogamy has been observed in par- 

 ticular in the flowers of Tofieldia and the Bog Asphodel (Narthecium). 



Even in upright flowers autogamy sometimes takes place in the second half 

 of their time of flowering through a fall of pollen, and that without any change 

 of position on the part of petals, stamens, or style. To make cross-fertilization 

 possible, in the first instance, flowers of this kind are protogynous. Subsequently, 

 after the dehiscence of the anthers, a portion of the crumbly pollen becomes 

 detached, and is deposited on the stigma below. In the case of erect flowers with 

 funnel-shaped corollas, the pollen slips down the smooth sloping wall of the funnel 

 to the stigma, and it is not essential for the anthers to stand vertically above the 

 stigma, since the corolla acts as a sort of conduit for the pollen. The Lilac 

 (Syringa) is an example of the plants of this category. It is also remarkable for 

 the fact that, though its flowers are only protogynous for a very short time, yet, 

 for one or two days after the dehiscence of the anthers, autogamy cannot take 

 place, because the anthers face outwards. So long as the anthers are in this 

 position the pollen cannot be transferred without extraneous aid to the corolla- 

 tube; it is not till later on, when the anthers get covered all round with pollen, 

 owing to the gradual shrinkage of their walls, that some of the pollen drops on to 

 the stigma standing underneath in the tube of the funnel. 



Very often in erect or obliquely ascending flowers autogamy is brought about 

 by an elongation of the filaments during the period of flowering, the result being 

 that the anthers, which are originally lower down than the stigmas, are elevated 

 to the same level as the latter, and are thus enabled to deposit their pollen upon 

 them. Most of the species belonging to this group are protogynous; the filaments 

 are erect, and are either adherent or else parallel to the ovary or style. At first 

 the anthers are so far from the stigma that the pollen would not of itself dust 

 the stigma in the same flower, but the subsequent elongation of the filaments 

 is so regulated as to carry the anthers to the same level as the stigma by the 

 time they are coated with pollen. The anthers then adhere to the receptive 

 stigmatic tissue, and autogamy is the result. The following are instances of plants 



