Sola?ium tubingense is a type of the periclinal chimera. Look- 
ing at it superficially, its characters appear to be intermediate 
between the two parent forms, but careful anatomical investiga- 
tion demonstrated that internally it was pure nightshade with an 
external covering of pure tomato cells. Other forms obtained 
were found to be of the same character, while in still other 
intermediate forms, the tissue areas were reversed, the internal 
area being tomato with an external coat of nightshade. In 
some of the chimeras, the external coat was two layers of 
cells in thickness, while in others there was only one layer. 
When seeds from these intermediate or periclinal forms were 
planted, either pure tomato or pure nightshade plants resulted, 
depending altogether on the nature of the internal tissue. Hence, 
seeds of Solanum tubingense produced pure nightshade plants, 
while the forms with internal tissue areas of tomato covered with 
an external layer of nightshade produced pure tomato plants. 
Dr. Erwin Baur, of Berlin, first suggested the possibility of 
explaining Winkler’s chimeras or graft-hybrids in this manner, 
as he had found in white-margined Pelargonium ( Geranium ) 
plants a somewhat similar state of affairs. 
There is still one other interesting aspect of plant grafting to 
be considered — that of its bearing on plant genealogy. Can one 
unite apple scions with Norway maple stocks or roses with pine 
trees? Decidedly not ! Theoretically, the nearer the relationship 
of scion and stock parent, the more successful the graft union. 
But how is one to determine this relationship? By taking the 
more or less superficial observations of the plant classification- 
ists or the data from the crossing experiments as a guide? If the 
data from these sources are good criteria, why do some varieties 
of plants grow better on the roots of other varieties than they do 
on their own — as, for example, Solanum nigrum erythrocarpum 
on the roots of the tomato, or certain varieties of pear on the 
roots of quince. Horticulturists tell us this is true in these 
cases, even when both grafted and ungrafted plants are grown 
under equally favorable growth conditions. And again, if cross- 
ing is a good criterion of relationship, why do hawthorn trees 
and cotoneaster bushes, lilac shrubs and ash trees, tomato and 
tobacco plants, plum and peach trees graft together with a fair 
degree of facility, when, so far as our present evidence goes, they 
cannot be successfully crossed? From what has been said, it 
would seem that an absolutely safe criterion for establishing the 
degree of relationship between plants is lacking. Consequently 
