CANNON: StTupDIES In PLant Hysrips 1438 
the later ones those of the other. For example, hybrid Zropeolum 
which was intermediate at the beginning of the season, reverted 
later to the mother form with intermediate grades * ; in spring the 
leaves of hybrid Czstus and Populus may show characters of one 
of the parents, and in the autumn those of the other; or in other 
hybrids (Melandrium album x M. rubrum, Epilobium roseum x E. 
montanum) the flowers may change during the blossoming from the 
characters of one parent to those of the other; or this may take 
place in different years (Bletia crispa x B. cinnabarina, Galium 
cinereum x G. verum). 
In another sort of hybrids the parental characters may reap- 
pear side by side —these are the so-called ‘ mosaic’ hybrids. 
They usually result from the union of closely related parents. 
As a single example of mosaic plant hybrids, that produced by 
crossing Rhododendron Rhodora x R. calendulaceum may be cited. 
In this case the flower has the colors of the flowers of both par- 
ents, and these are reproduced unchanged and stand side by side. 
Darwin + gives an example of an interesting mosaic animal hybrid. 
He says “the hairless condition of the Paraguay dog is either per- 
fectly or not at all transmitted to its mongrel offspring ; but I have 
seen one partial exception in a dog of this parentage which had 
part of its skin hairy, and part naked; the parts being distinctly 
Separated as in a piebald animal.” 
Occasionally the hybrids are invariable and come true to seed. 
Such a one is the Oenothera hybrid of de Vries,{ formed by the 
union of O. rubrinervis and O. nanella, which has been grown 
several generations without reversion. Another eae ey be 
mentioned out of many, namely, that of the Geum hybrid already 
referred to. This plant is a natural hybrid in ceria parts of 
England, and was formerly supposed to be a distinct —— 
Salter § reproduced the hybrid by crossing G. ” vuale and G. 
urbanum. All of these hybrids were uniform and intermediate, 
and came true to seed for many generations. 
Still another class of inheritable characteristics may well be 
mentioned ; I refer to the transmission of such characters as hardi- 
~~"¥ Darwin, Animals and Plants Under Domestication, Am. ed., 2: 470. 1868, 
ft Darwin, 7. ¢. 2: 117. 
{ De Vries, Die Mutationstheorie, 1: 461. I9g0I. 
§ Salter, 7. ¢. 739. 
