THE ANGIOSPERMAE 1331 



an insect, already bearing pollinia on its head, visits a flower in this stage, 

 pollen will be deposited on the stigma as the fly reaches the top of the 

 groove. Flowers on the same inflorescence can be found in various stages 

 of development, but there appears to be appreciable cross-pollination 

 between different inflorescences as well. 



ii. Lepidopteroiis Flowers 



Flowers visited by butterflies and moths are characterized by very long 

 corolla tubes, such that the nectar can be reached only by insects with very 

 long tongues. The length of this organ varies considerably in the different 

 insect genera and some of the most eflicient pollinators belong to those 

 genera with the longest tongues, as for example the Hawk Moths and some 

 of the larger butterflies. Occasionally, instead of long narrow corolla tubes, 

 the nectar may be secreted in special pockets, as in the case of Liliiim mart- 

 agon (see also Fig. 1245, P- i344)- While a bee must collect steadily all the 

 available nectar to store up for the use of its colony, a butterfly need only 

 settle on a flower if it feels the need of food. Hence attraction may play a 

 far more important part in the visits of these latter insects. Many ot the 

 flowers visited by butterflies are pink, red or violet in colour, but the total 

 number regularly visited, as distinct from those settled on occasionally, 

 is quite small. Miiller, for example, was only able to record 33 true butterfly 

 and moth flowers in the whole alpine flora. Moth flowers are in many 

 respects quite different from butterfly flowers; many open only at dusk and 

 rely upon night-flying moths for pollination. Such flowers are usually white 

 or light in colour so that they are readily apparent in the dusk. 



(a) Butterfly Flowers 



Flowers which are regularly visited by butterflies are either red or violet 

 in colour and as a rule the flowers stand erect, for pendulous flowers are 

 rarely visited by them. For example, the orange-red Liliiim philadelphiciim 

 has large, open, upright flowers and the perianth segments are contracted 

 at their bases, leaving openings between them, so that rain-water drains away 

 and does not collect in the base of the flower. The stamens and stigma 

 project a little above the level of the perianth, while nectar is secreted in 

 grooves formed on the perianth segments. The butterfly therefore can alight 

 easily on the broad limb of the petal and run its tongue down the groove to 

 the nectar. In contrast to this is Liliiim canadense, in which the flower is 

 pendulous, with broad overlapping perianth segments, which serve to 

 throw the rain ofl" the flowers. This flower is pollinated by bees, which 

 alight on the stigma and crawl up the style to the nectar, which is secreted 

 at the base of the flower. Such a flower would be quite unsuitable for butter- 

 flies, for it does not provide a suitable alighting platform for an insect of 

 their shape. Moreover, while the anthers of L. philadelphiciim are versatile 

 and covered all over with pollen, those of L. canadense are fixed in one 

 position. 



It has been repeatedly pointed out that there is a marked correlation 



