PLANTS WITH EXTRAFLORAL NECTARIES. 67 
floral nectar glands, which have been noticed by systematic as well 
as by physiological botanists (Baillon, Miller Arg., Bentham and 
Hooker). They are found on the stipules of Jatropha multifda, and 
on the petiole at the base of the leaf blade of Aleurites moluccana. In 
a paper by Perey Groom on the extrafloral nectaries of the allied 
Aleurites cordata” these petiolar nectaries are described as follows: 
fach nectary is a green-stalked shallow basin, the concavity of which is tinted red. 
The secreting cells which line the basin form a single layer of palisade-like cells. 
The general cuticle is preserved over these, and the secretion emerges through splits 
init. The main body of the basin is composed of an anastomosing system of con- 
ducting parenchyma and ground parenchyma. * * * The secreting cells contain 
proteids, sugar, a red coloring matter (a compound of tannin?), tannin, but no 
starch. In the ground parenchyma starch, tannin, and crystals of calcic oxalate 
occur, The conducting parenchyma contains sugar, but no starch or crystals. 
* * * Darkening the nectaries of leaves on the plant or of excised leaves, or 
darkening the whole leaves, caused a gradual disappearance of the starch, but the 
nectaries continued to excrete for a time. 
The above description applies very nearly to the stipulary nectaries 
of Ricinus, a photograph of a cross section of which, made by Mr. 
B. J. Howard, of the United States Department of Agriculture, is 
shown in Plate LX, fig. 1. 
Among the Malvaceae growing in Guam several are provided with 
nectar glands on the underside of the midrib. These are most con- 
spicuous in Urena sinuata, occurring not only on the midrib, but some- 
times on the main lateral ribs of the palmate leaves. They also occur 
on all leaves of cotton (Gossypium sp.) and on the midrib of Parct: 
tiliaceum (PL. X, fig. 2), in the form of vaginate glands. A photo- 
graph of a cross section of the nectar gland of a cotton leaf, also made 
by Mr. Howard, is shown in Plate X, fig. 1. 
The sweet fluid secreted by these glands is eagerly sought by sugar- 
loving insects, and a number of authors maintain that the power of 
secreting it has been specially gained by plants for the sake of attract- 
ing ants and wasps, which will serve as defenders against caterpillars, 
leaf-cutting insects, or other enemies; but Darwin,? after a series of 
observations, could not see any reason to believe this to be so with the 
species observed by him, although the fact that these glands are 
visited by insects for the sake of their nectar can be verified at any 
time of the day when the sun is shining, and these insects must serve 
as a protection for them. It is interesting to note that these glands 
may occur in one species and be absent from another closely allied to 
it of the same genus. Indeed, there are species in which the glands 
are present on some leaves and absent from others, and of their vari- 
abilitv we have already spoken in connection with Ricinus and Urena. 
¢ Annals of Botany, vol. 8, p. 228, 1894. 
4Cross and self fertilization, pp. 4038, 404, 1877. 
