AN UNUSUAL BEGONIA. 
13 
occurring in Mexico, this species grows further north than any 
of its near relatives, the so-called tuberous begonias, most of 
which come from the Bolivian and Peruvian Andes and some 
of which are now popular in cultivation; second, and for this 
reason especially, the plant has a peculiar habit of growth. 
Begonia unifolia possesses a single, large, flat, orbicular leaf 
which is sessile on the underground stem and is therefore closely 
applied to the ground. Through the sinus in the leaf rises the 
flower stalk bearing both pistillate and staminate flowers which 
are white in color. 
This single leaf lying flat upon the ground recalls a similar 
habit in several species of Streptocarpus, in which one of the two 
cotyledons enlarges greatly and spreads out as a gigantic foliage 
leaf, while the plant develops no other leaves. The staghorn fern 
(Platycerium) , common in large greenhouses, likewise develops, 
besides its forked, antler-like fertile fronds, one or two green disk¬ 
shaped sterile fronds which resemble immense prothallia and re¬ 
main always at the base of the plant. Since this fern grows 
naturally on tree-trunks in tropical forests, these broad basal 
leaves doubtless aid in retaining moisture for the roots and collect 
also organic materials. 
In the case of this Begonia described by Professor Trelease, 
growing as it does on steep, rocky, canon walls, possibly this low, 
broad leaf performs the same functions—providing protection for 
the subterranean parts and helping to retain the moisture and 
organic materials which pass its way. Ada Watterson. 
Under the title “A New Conception Concerning the Origin 
of Species ” Professor Hugo de Vries gives in Harper's Monthly 
Magazine for January, a personal account of the way in which 
the author was led to make his experiments which led to the 
formulation of the Mutation Theory of the Origin of Species. 
In Science, 20: 395, September 23, 1904, Professor de Vries 
published another important communication on the “ Evidence 
of Evolution,” in which he considered in a broad way the Dar¬ 
winian concept of descent, and its relation to the Mutation Theory. 
He there “ intimates that the real significance of the newer ideal 
lies not so much in its substitution for the older, as in its impor¬ 
tance in pointing out new lines of research.” 
