flowers were examined as to (a) original position of the stigma with respect to the mouth of the floral tube; (b) final position of the stigma; (c) position of stigma at which pollination is successful in initiating fertilization; (d) the degree of inhibition of style growth due to pollination. Careful observations were necessary for this part of the study. Pollination was found to inhibit most of the growth of styles in both females and hermaphrodite flowers, and furthermore the stigmas were found to be receptive to pollen (resulting in fruit set) over a limited period. This extends for 1–3 days after the flowers open and they begin to wither within a week. When female flowers open the stigma is just above the mouth of the flower tube, but in the hermaphrodite it is still below the mouth of the tube (about a third of the way down it). Growth of the style is continuous after the opening of flowers unless pollination occurs, when the growth is slowed down. In the hermaphrodite during the 1–3 days when successful pollination can occur the stigma is below the level of the mouth of the flower tube. Once the stigma is exserted beyond this, fertilization cannot occur although pollination still inhibits most of the growth. In some cases it was found that pollen from one species is capable of halting style growth of another species. P. prostrata pollen on P. “snow tussock” stigmas and P. “snow tussock” pollen on P. prostrata stigmas was found to act in this way. This inhibition of style growth holds for both female and hermaphrodite flowers but fertilization of the latter is more rare. If unpollinated, the style of hermaphrodite flowers may eventually grow to nearly twice the length of the floral tube. Female styles rarely grow to more than one and a-half times its length in the same circumstances. Because of this it is possible to see in the field which flowers are pollinated although this is not a direct measure of fertilization and fruit set. A high proportion of hermaphrodite flowers in the field were noticed to be unpollinated.

Growth of the style is important mainly in connection with selective influences in the breeding system. Because of differences in stigma and stamens, both in gross structure and, in their position within the floral tube when mature and because of the short time of their receptivity to pollen, it may be shown that a situation favouring cross pollination is present in Pimelea. The floral tubes in female and hermaphrodite flowers are of differnt length and styles of about the same length when the flowers open. (Fig. 1.) The implications of this, as concerns the insects involved and cross pollination are as follows. The insects visiting female and hermaphrodite flowers when both are functional will be more effective in corss pollination between sexes than in self pollination of hermaphrodites (although some self pollination of or crossing between hermaphrodites may be brought about by insects). This situation is dependent on the hermaphrodite stigmas being receptive to pollen only when low down in the floral tube. Insects will not normally carry pollen to these stigmas. They are not receptive when they are exserted, which occurs when they grow older (if not pollinated). Position of receptive stigmas in females relative to anther position in hermaphrodites, together with larger papillae on female stigmas, which pollen adheres to more readily, encourages outcrossing between sexes. Crude tests consisting of rubbing a clump of pollen grains on a needle against both female and hermaphrodite stigmas showed that pollen stuck to the larger female papillae more easily. Natural selfing of hermaphrodites without aid of insects, can and does occur as was shown experimentally, but this is rare. From the flower count and fruit set data it is seen, however, that a significant small percentage of hermaphrodite flowers set fruit in all the taxa. This must result largely from cross fertilization, and ensures that a number of fruit are set in hermaphrodites. Presumably there is some physiological barrier, genetically controlled, which prevents a very high percentage of hermaphrodite fruit set. This needs further investigation, although genetic experiment in Pimelea is a long term project. The females, however, set fruit freely in all species.