59 



FLOWERS AND THEIR INVITED GUESTS. 



It must be taken for granted in this 

 paper that the reader has such knowledge 

 of the parts of the fiower as could be ob- 

 tained from the paper on "A Typical 

 Flower," printed in the June number. 



When flowers first appeared it became 

 necessary to secure the transfer of the 

 pollen grains to the stigmas. This was 

 necessary in order that the ovule might 

 be developed into a seed containing a 

 young plant or embryo. At first the cur- 

 rents of air were selected as the agents 

 of this pollen transfer, and the flowers 

 were adapted to what is known as wind- 

 pollination. As the wind is an inanimate 

 agent any transfer by. it is largely a matter 

 of chance. In order to increase the 

 chances of successful pollination it was 

 necessary for pollen to be developed in 

 enormous quantities, so that it might fall 

 like rain. In this way stigmas would be 

 reached, but at the same time an enor- 

 mous amount of pollen would be wasted. 

 The evergreens are good illustrations of 

 wind-pollinated plants, and their showers 

 of pollen are very familar to those who 

 live near pine forests. When these show- 

 ers come down in unaccustomed regions 

 they are often spoken of as "showers of 

 sulphur," and the local newspapers are 

 full of accounts of the mysterious sub- 

 stance. 



In wind-pollinated plants not only must 

 the pollen be excessively abundant, but 

 it must also be very light and dry. Some- 

 times the buoyancy is increased by the 

 development of wings on the pollen 

 grains, as in the case of pines. This habit 

 of pollination is found not only among 

 the evergreens, but also among many im- 

 portant families of the higher plants, as 

 in the ordinary forest trees, the grasses, 

 etc. 



When the higher forms appeared, how- 

 ever, flowers of a different character gave 

 evidence that a new type of pollination 

 was being devised. Instead of the old 

 wasteful method, insects were called in to 

 act as agents of the transfer. By securing 

 an animate agent there is a definiteness in 

 the pollination and a saving in pollen pro- 



duction which is quite in contrast with 

 the wind method. It must not be sup- 

 posed that all flowers have learned to use 

 insects with equal skill, for many of them 

 may be said to be clumsy in their arrange- 

 ments. On the other hand, certain fami- 

 lies have reached a high degree of organi- 

 zation in this regard, and arrange for in- 

 sect visits with a skill and completeness 

 of organization which is astonishing. 



In order to secure visits from insects, 

 so that pollination may be effected, 

 flowers have been compelled to do several 

 things. In the first place, they must pro- 

 vide an attractive food. This has taken 

 two prominent forms, namely, nectar and 

 pollen. There are insects, such as butter- 

 flies, which are not only attracted by the 

 nectar, but whose mouth parts have only 

 been adapted for sucking up a liquid. 

 There are other insects, however, like the 

 bees, wasps, etc., which are able to take 

 the more substantial pollen as food. Ac- 

 cordingly insects which visit flowers may 

 be roughly divided into the two classes, 

 nectar-feeders and pollen-feeders. 



In the second place, the flower must 

 notify the insect in some way that the 

 food is present. This is done primarily 

 by the odors which flowers give off. It 

 must not be supposed that odors which 

 are sensible to us are the only ones sensi- 

 ble to insects, for in general their sense 

 of smell is far keener than ours. It is also 

 probably true that the display of color, 

 which is so conspicuously associated with 

 flowers, is an attraction to insects, al- 

 though this has become somewhat doubt- 

 ful lately by the discovery that certain 

 insects which were thought to be attract- 

 ed by color have proved to be color blind. 

 At present, however, we have no reason 

 to suppose that color is not associated in 

 some prominent way with the visits of 

 insects. 



It should be noticed, also, that two 

 kinds of pollination are possible. The 

 pollen may be transferred to the stigma of 

 its own flower, or it may be carried to i he 

 stigma in some other flower, and this 

 other flower may be some distance away. 



