136 THE STORY OF THE PLANTS. 



of them separately, and of the work they do in 

 getting the seeds set. Incidentally, however, it 

 has been necessary at times to touch slightly upon 

 the way they often mass themselves into heads 

 or clusters for various purposes; and we must 

 now begin to consider more seriously the origin 

 and nature of these co-operative societies. 



Very large flowers, like the water-lily, the 

 tulip, the magnolia, the daffodil, are usually soli- 

 tary ; they suffice by themselves to attract in 

 sufficient numbers the fertilising insects. But 

 smaller flowers often find it pays them better to 

 group themselves into big spikes or masses, as 

 one sees, for example, in the foxglove and the 

 lilac. Such an arrangement makes the mass more 

 conspicuous, and it also induces the insect, when 

 he comes, to fertilise at a single visit a large num- 

 ber of distinct blossoms. It is a mutual conven- 

 ience ; for the bee or butterfly, it saves valuable 

 time; for the plant, it ensures more prompt and 

 certain fertilisation. In many families, therefore, 

 we can trace a regular gradation between large 

 and almost solitary flowers, through smaller and 

 somewhat clustered flowers, to very small and 

 comparatively crowded flowers. Thus the largest 

 lilies are usually solitary or grow at best three or 

 four together, like the lilium ainatum ; in the 

 .tuberose and asphodel, where the individual blos- 

 soms are smaller, they are gathered together in 

 big upright spikes; in the hyacinth, the clustering 

 is closer still ; while in wild garlic, grape-hya- 

 cinth, and star-of-Bethlehem, the arrangement 

 assumes the form of a flat-topped bunch or a 

 globular cluster. Of course, small flowers are 

 sometimes solitary, and large ones sometimes 

 clustered ; but as a general rule the tendency is 



