THE AMERICAN BOTANIST. 85 



Ants and Seed-Dispersal. — We seldom think of insects 

 as distributors of seeds of plants. In the arrangements for pol- 

 lination insects hold first place, but the plants usually bid for 

 larger assistants, such as mammals and birds when their 

 seeds are to be scattered. There are very many adaptations 

 in the fruits of plants that make the conclusion irresistable 

 that they were intended to entice animals to distribute the 

 seeds. Few if any modifications which would cause seeds to 

 be distributed by ants have been noted though some are in- 

 clined to think the caruncle of seeds like the bloodroot is an 

 adaptation to make them easy for the ants to grasp. It is 

 well known, however, that ants are great gatherers of seeds. 

 The most of these are carried off and eaten, but probably as 

 great a proportion are dropped and forgotten as of the hickory 

 nuts carried off by the squirrels. Among the seeds that ants 

 are most fond of may be mentioned shepherd's purse, chick- 

 weed, fumitory, nettle, snap-dragon, flax, cress, pigweed and 

 various grasses. 



Heliotropism of the Water Fern. — The curious fact 

 that the water fern {Marsilia) like the clover and oxalis, 

 closes its leaves at night, has long been known, but Robert F. 

 Griggs has recently noted what appears to be a new motion 

 of the leaves to enable them to face the sun. Thus far the 

 habit has been noticed in but one species, M. vcstita, but it is 

 likely that other species may be found to act in the same way. 

 According to the writer quoted, the leaves at evening squarely 

 face the west, while shortly after sunrise they will be found 

 to face the east. The movement seem to be produced by the 

 petiolules of the individual leaflets, rather than by the petiole 

 of the leaf. The motion which causes the closing of the leaves 

 at night is also located in the petiolules. One striking differ- 

 ence between the night position of marsilia and oxalis leaves 

 is that in the former the leaflets are erect and in the latter the 



