382 GENETICS IN RELATION TO AGRICULTURE 
to a single variegated specimen of Abutilon striatum Dicks., which was 
introduced into Europe in 1868 and named Abutilon thomson. Miss 
Reid has shown, however, that among the flowering maples (Abutilon) 
the variegated forms can be grouped into two classes: “those with a 
mottled variegation which is infectious and those with a non-infectious 
variegation with the white cells at the periphery. Both types are of 
importance in horticulture, especially for use as bedding plants; both 
types are of special scientific interest.” 
The Physiological Behavior of Graft-hybrids.—Although chromosome 
counts and progeny tests indicate that the cells of each graft-symbiont 
maintain their identity independently of the close proximity of foreign 
cells, yet the intermediate characters of graft-hybrids indicate that the 
components have a mutual influence upon each other. This influence 
is especially notable in the manifestation of physiological activity in- 
volving the whole plant. None of the Solanum graft-hybrids are as 
vigorous as either component under normal conditions. In fact, it is 
with considerable difficulty that they are maintained by means of cut- 
tings, except in the case of Koelreuterianum. - This lack of vegetative 
vigor may not be characteristic of all graft-hybrids but it seems to be 
common to most of them. Lack of vigor exists in many natural chimeras 
also, especially in those involving chlorophyll reduction. 
In the Solanum graft-hybrids the germ cells of the two components 
are not equally susceptible to the effect of adjacent foreign cells. In both 
tubigense and Gaertnerianum the fruits contain fertile seeds which pro- 
duce only pure nightshade plants. But in proteus only part of the seeds 
are viable and these produce tomato seedlings, while in Koelreuterianum 
the flowers are entirely sterile. Similarly, in Cytisws Adami the ‘‘hybrid”’ 
(intermediate) flowers are sterile. 
Graft-hybrids offer many interesting possibilities as a means of studying 
the physiology of development as influenced by the reciprocal relations 
between the components. This method of attack has been utilized much 
more extensively in the study of development in animals than in plants. 
Crampton, for example, grafted together the pup of different species 
of moths thus producing double monsters. From the specific effects 
upon pigmentation in some of the graft symbionts it was concluded that 
the pigmental colors in some species are derived from the haemolymph 
by processes of drying and decomposition which are regulated by some 
specific internal factor. Crampton mentions several other investigators 
who performed similar experiments on animals. Buder has suggested the re- 
ciprocal grafting of male and female plants in dicecious species as a means of 
investigating the physiology of sex determinationin plants. This suggests 
the whole field of reciprocal effects between scion and stock, concerning 
which there has been considerable investigation in recent decades. 
Digitized by Microsoft® 
