AMERICAN HONEY PLANTS 173 



make these nests in the stipules that flank each leaf and sometimes are 

 shaped like a pair of small buffalo horns. It is an interesting undertaking 

 to get the ant census of an acacia twig of this sort. The danger may not 

 be as great, but it is as real and perhaps as painful as in taking the cen- 

 sus of a mountain valley noted for moonshine traffic. 



Belt drew the conclusion that extranuptial nectar, sometimes supple- 

 mented by solid food and shelter, is of use to the plant that provides it by 

 maintaining a bodyguard of ants on plants that otherwise would be de- 

 foliated and injured by leaf cutters or grazing animals, much as Sprengel 

 and Darwin found an explanation of nuptial nectar in the benefit of insect 

 poUinization of the flowers. 



This is the simple story of nectar, simply told, as it has been seen by 

 observing and thinking men. But it is not a story free from complications. 

 Our blue violets rarely set fruit from their showy nectar-bearing flowers, 

 but their main reliance for seed is on flowers produced below the leaves, 

 and these do not open, but are self-fertilized. The beautiful Poinsettia, 

 with its brilliant red bracts and large cups overflowing with thick nectar, 

 does not fruit in West Indian gardens any more than it does in our green- 

 houses at Christmas time. And irresistibly pugnacious as the acacia ants 

 are, those that visit our paeonies and cassias and other plants do not usu- 

 ally more than protest mildly if we molest the plants that they are on. 



Are the explanations of Sprengel and Darwin, and of Belt wrong? No 

 other that are at all satisfactory have been offered. 



When one stops to think of it, the secretion of nectar is an ususual phe- 

 nomenon. Sugar is made within plants and it does not leak from them un- 

 less they have been injured. The sugar beet takes various substances out 

 of the soil water, but it does not permit the passage of sugar into the soil 

 water. And yet nectar, essentially sugar, is passed out of the plant, within 

 which it was manufactured. This is because it is secreted — or excreted — 

 through specialized glands. Everyone who grows plants in a bay window 

 has seen young clover or grass leaves with a drop of water on their tips at 

 some time or other. A few grains of bird seed in a flower pot covered by 

 a pane of glass will show this as quickly as the seedlings come up. 



These drops pass out finally through pores; but they are drops of water 

 and not of nectar. If we can imagine a gland behind such a water pore, 

 secreting sugar— letting it really get out of the cells with or into the water, 

 we can picture a nectar gland. Such glands occur in some flowers. Some 

 botanists believe that extranuptial nectar glands were originally water 

 glands that have acquired the habit of secreting sugar. 



This habit is a very unusual and a very peculiar one. It is not really 

 understood except as it may be connected with usefulness to the plant. If 

 this usefulness is not indirect, in the wa3^s suggested by Darwin and Belt or 

 otherwise, it must be direct. Water glands relieve over-pressure when ab- 

 sorption is high and evaporation low; in some of the calla family the 

 water even spurts from the tips of the leaves at times. But sugar is not 

 like water, taken in in quantity and to spare ; it is manufactured, and in 

 the case of nectar glands it is manufactured where it is secreted. Nobody 

 has yet suggested any physiological function of plants calling for sugar 



