MEXICAN AND CENTRAL AMERICAN SPECIES OF SAPIUM. 161 
This is, I believe, enough to show on the one hand that the appar- 
ent scarcity of Sapium species in and north of Costa Rica must be 
attributed mainly to our deficient knowledge of the flora, and on the 
other that there is really no reason why some of these unknown or 
little-known Central American species should not also be found to 
yield commercial rubber. It is in anticipation of further researches 
on the subject that the present revision of the species known from 
Middle America has been undertaken. 
In the preparation of this paper I have used the material in the 
United States Nationai Herbarium, and also in the collections that 
were kindly loaned me by the Gray Herbarium, the Field Museum 
of Natural History, Capt. John Donnell Smith, of Baltimore, and 
the Instituto fisico-geogratico, of Costa Rica. The last collection con- 
tained no less than seven new species, five of which had been named, 
although not described, by Dr. Karl Schumann, Although it is not 
unlikely that upon further investigation the number of these Costa 
Rican species will need to be reduced, I prefer to maintain here 
the specific divisions established by the lamented Berlin botanist. 
Not long ayo one of the forms distinguished by him under the name 
of S. pycnostuchys was described by Huber,” who gave it the less 
desirable name of S. pittier?. 
Regarding the general systematic treatment of the genus Sapium, it 
must be said that it is still very imperfectly known. Not only are the 
differences between the numerous species often very vaguely defined, 
and many species have been included under one name, but even the 
limits of the genus do not seem to be always understood, as there has 
been a continual confusion between Sapium, Excoecaria, Sebastiania, 
and Stillingia.’ This is due, without doubt, to the absence in most 
herbaria of sufliciently extensive material. 
“Bull. Herb. Boiss. IT. 6: 350. 1906. 
’As understood to-day, the genus Excoecaria is limited to the Eastern Hemi- 
sphere, with /. agallocha as the type species. It differs from Sapium by characters 
of seemingly little importance and perhaps not yet well defined. Most of the species 
are dicecious; the divisions of the male calyx are distinct, very narrow, and usually 
three in number; the clusters of the male flowers and the pistillate flowers are pedi- 
cellate, each cluster of the first seldom containing more than three flowers; the seeds 
are smooth. Mueller of Argau (in Mart. Fl. Bras. 11°: 611-630) includes all the 
American species in this genus, of which Sapium is then only a subdivision. But 
this view has not been sustained by Bentham and Hooker and the more recent 
writers. 
Sebastiania is alsoa very near related genus, mostly from extratropical America. It 
differs at first sight from Sapium by the reduced size of the plant, the absence of 
petiolar and bracteal glands, the smooth seeds, and the bivalvate dehiscence of the 
capsules. In Stillingia, another member of the same group, we note the absence of 
the persistent axial column of the capsule and marked differences in the glandular 
apparatus; also the American species of that genus are mostly extratropical and 
somewhat distinct in their habits. 
514386—08——? 
