i26o A TEXTBOOK OF THEORETICAL BOTANY 



Humble Bees have not the same responsibihties as the Hive Bee for 

 large honey stores and some of the species are monotropic. For instance, 

 both Hive Bees and Humble Bees visit the flowers of Salix, for pollen and 

 nectar, but four species of the big genus Andrena get the whole of their 

 supplies from this genus alone. In the big North American genus Perdita, 

 all the species are monotropic, one species of bee going only to one species 



of flower. 



Certain flowers, whether producing nectar or not, are frequented prin- 

 cipally, and in the latter case exclusively, for their valuable stores of pollen, 

 which is used by the bees for brood-rearing. Such flowers are: Clematis, 

 Anemone, Papaver, Thalictrum, Hypericum, Taraxacum, Sambucus and 

 Cistiis. They may have coloured corollas, but in some, like Salix, Thalic- 

 trum or Metrosideros in New Zealand, it is the prominent, coloured stamens 

 which are the flowers' chief visible attraction. In all these flowers the 

 stamens are so numerous and the production of pollen is so far in excess of 

 the amount required for pollination, that the sacrifice of even large quanti- 

 ties does no injury to the flowers, provided that the pollen-dusty bee will 

 come and scramble over the waiting stigma. The loads of coloured pollen 

 which burden the returning bees at certain seasons are the best evidence of 

 the satisfaction of both parties to the arrangement ! Pollen yields the bees 

 their chief protein ration. A full-grown colony requires between 44 and 70 

 lbs. in a season. 



Given that the pollen is plentiful in the flowers they frequent, the bees 

 prefer it to be small-grained and rather dry. They moisten it as they pack 

 it, with honey they provide themselves. Large and sticky grains embarrass 

 the pollen collectors and are not popular with them, although such types 

 of pollen are easily picked up by the nectar-sucking visitor and conveyed 

 by it as an unintentional incident of its routine. 



Pollen-flowers are generally actinomorphic and flowers of this form are 

 usually held vertically and are fully open. Many nectar flowers are in the 

 same category, but zygomorphic flowers are practically all nectariferous, and 

 such flowers are generally held horizontally or are pendulous. In either case 

 there is often some structural provision which protects the nectar, and, not 

 less importantly, the pollen, so that it is not too much exposed either to 

 robbery by small and useless flies or to wastage by stormy weather. Even 

 in the open and actinomorphic flowers the nectar may be concealed at the 

 base of the ovary as in Clethra, or arched over by the bases of the stamens, 

 as in Campanula, or by the connivent anthers, as in Solanum, or concealed by 

 flaps of tissue, as in Ranunculus, or held in specialized nectar grooves, as on 

 the petals of Lilium, or in special nectar-holders, as in Helleborus and Nigella. 

 Finally the whole flower may be pendulous, as in Fuchsia, Atragene and 

 Soldanella. The last-named also possesses a ring of scales, below the inser- 

 tion of the stamens, which shuts ofl^ a chamber containing the ovary, and 

 in which the nectar is concealed. Flowers with a narrow entrance to the 

 floral tube may partially occlude the entrance, either with the enlarged 

 stigma (pin-eyed Primula and some species of Gentiana) or with the anthers 



