May 1907. ] 



■>W) 



MISCELLANEOUS. 



Lessons in Elementary Botany, IX. 



By J. C. Willis. 



Floral Mechanisms.* — Tt is evident that if a visiting insect is to be of any 

 use in carrying pollen to the stigmas, that part of its body that touches the pollen 

 must also touch the stigma. Tliis is simple enough when the male and female 

 flowers are separate, but in the vast majority of plants the flowers are both male 

 and female. In order that both may touch the insect at the same, or nearly the same 

 point, the anthers and the stigma must be placed near together, and the various 

 ways in which this is done without at once causing self-pollination are of some 

 interest. 



Male and female flowers occur in a good many upcountry plants, but this 

 method of separation is rare. 



Heterostylism, or the possession of two forms of flowers, one with long and 

 one with short style, is not uncommon. The common patana herb, Knoxia piaty- 

 carpa, with its white or pinkish flowers, open all the year round, shows this 

 phenomenon very clearly. On one plant all the flowers have a long style sticking 

 out of the corolla, while the stamens are hidden, and on another plant only the 

 stamens stick out, and the style is hidden. Now it is found that in the case of a 

 plant like this, good seed is only set if pollen be taken from a long stamen to a long 

 style, or from a short stamen to a short style, i.e., from one plant to another, and it 

 is obvious that insects will be more likely to do this, provided they go to several 

 plants, than to take pollen from a short stamen to a long style, or from a long to a 

 short. Illegitimate pollination, as the latter is called, usually results in no seeds 

 being set at all, or only very few and infertile ones. 



Perhaps the most widespread arrangement is what is called dichogamy or 

 separation of the sexes in time, the stamens being ripe first, the stigma afterwards, 

 or vice versa. This is extremely common, and is usually accompanied by a 

 movement of the parts, so that at one time the stamens, at another the style, stand 

 in the way of the visiting insect. Most of the plants of the family Compositae 

 (daisies, dandelions, chrysanthemums, and similar plants), for example, are what is 

 called protandrous (male first), the stamens being vipe before the stigma, which 

 comes up through the tube made by the anthers, pushing out the pollen at the top. 

 Later on the stigma emerges, and opens out, but by this time all the pollen has gone. 



Another very common, but less perfect arrangement is that while the stamens 

 and style stand very near together, the latter projects a little further out, so as to be 

 first touched by the visiting insect, which may rub off upon it any pollen that 

 it canues. 



Yet another common arrangement is what may be called " loose-pollen, " the 

 pollen being held in a kind of box formed by the anthers, and shaken out upon the 

 head of any insect visiting the flower. The style in such a flower visually projects 

 further than the stamens. 



*Some illustrative figures will be giv«n next time. 



