1906] CURRENT LITERATURE 359 
a greater resemblance to the species furnishing the stationary or ‘“mother-”’ 
nucleus. 
The investigation shows that neither stock nor scion is itself of hybrid origin 
and that there can be no reasonable doubt that these are true graft-hybrids. 
The only other similar case that has attracted much attention is that of Lab- 
urnum (Cytisus) Adami, and about this plant there has been so much contention 
that, in the absence of other authentic graft-hybrids and with the disappearance 
of the original tree, it seemed best to many botanists to consider the original obser- 
vation and record to be in error. Nott prints the original account in full, and 
decides, after considering the possible sources of error and misinterpretation, 
that the internal evidence in favor of this statement compels belief in its truth. 
The final demonstration must lie in a reconstruction of the same ora similar 
hybrid, experimentally, and on this work Nott has been engaged for a number 
of years, as yet with wholly negative results; but the rarity of the phenomenon 
makes this quite to be expected, and the author still hopes by improving his 
technic to succeed in re-creating Laburnum Adami.—GrorcE H. SHULL. 
Experimental variation —K.rss' presents a paper which deserves special 
attention because of the experimental data recorded, because of the author’s 
effort to make a closer analysis of the problem of experimental variation, and 
because a substitute for DE Vrres’s intracellular pangenesis is offered. Long 
experience with the behavior of algae and fungi under artificial conditions, prob- 
ably as much as the results stated in this paper, has convinced the author that in 
the last analysis all variations must be referred to the influence which external fac- 
tors exert upon the inherent potencies of the organism. From this point of view 
the fundamental problem of experimental variation at once appears to be to deter- 
mine the potential amplitude of variation for species. This problem is to be solved 
by the application of as great a variety of conditions as possible. Some of those 
used by the author are temperature, darkness, wounding, and artificial food. 
The results obtained with Campanula trachelium and Sempervivum Funkii show 
that the accepted taxonomic limits of a given species are easily transgressed when- 
ever external conditions favor the expression of potencies inherent in the organism. 
Trial clearly shows that the potency of external conditions is much greater before 
the inception of organs than after. If, for example, nutrition is the determining 
factor for a given variation, it makes little difference whether the necessary nutri- 
tion status is established by one external condition or another 
Over one hundred pages are used to expound the author’s view of the cor- 
relation of variation and environment and to present a polemic criticism of intra- 
cellular pangenesis. The results with Sempervivum Funkii show that those 
characters which can appear as specific within the genus can by proper method 
be induced to appear upon a single species. A species therefore is to be 
4 KLEBS, GEorG, Ueber Variationen der Bliiten. Jahrb. Wiss. Bot. 42: 155-320. 
pl. 1. figs. 27. 1906 
