4 
4 
2 
4 
Fe eee ee ne es ee ee 
1906] CURRENT LITERATURE 67 
has the power of changing the gray pigment to black, but this pigment-changing 
unit will remain invisible so long as the albino is bred only with other albinos. 
Under this conception the novum is a compound character formed by the 
combination of equivalent units, instead of a hitherto inactive character ren- 
dered active by the stimulating effect of a foreign plasma. TscHERMAK?° now 
assents to the explanation of CuENoT and Correns as valid in certain cases, 
but still maintains that the nova of his Pisum arvense X sativum crosses and others 
cannot be so explained, because he found no cases in which the offspring were not 
all cryptomeric. TsCHERMAK’s reference to the fact that the mova are fre- 
quently of atavistic nature, as lending support to GALToN’s “law of natural inheri- 
tance,’’ will scarcely be approved, since the explanation of CUENOT and CORRENS 
would bring these into agreement with typical Mendelian hybrids. 
BatEson** has likewise adopted the explanation of CUENOT and CORRENS 
in the interpretation of mova in sweet peas and stocks which had been pre- 
sented’? in the Second Report to the Evolution Committee, as wholly out of 
harmony with Mendelian inheritance. These now constitute exceptionally good 
examples of characters which can only become manifest when two or more 
units act together. The statement is made that most of the five gametically 
distinct types which should appear among the white sweet peas and white stocks 
of these crosses have been recognized, thus answering satisfactorily, in respect 
to these two species, TscHERMAK’s contention that the extracted whites were 
still cryptomeric. 
he same explanation is clearly valid for the case reported by CasTLE? 
in which a white guinea- pig crossed with red gave rise to some black offspring, 
while the “extracted” whites from this cross, when crossed with red, produced 
no black young—Grorce H. SHULL 
Welwitschia—The full paper on Welwitschia mirabilis by Parson has 
now appeared,?4 the abstract of last November having been noted in this journal.’s 
The region of this strange plant is so difficult of access that Professor PEARSON 
is to hes commended for the unusual efforts he has put forth to secure eae 
As it happened, fee war in Africa has seriously interfered with his 
that he was able to secure material of only one day’s collecting, but he hopes 
that when the Siectig becomes more settled he will be able to fill in the gaps. 
ts 
° TSCHERMAK, E., Die Mendelsche Lehre und die Galtonsche Theorie vom 
— Arch: & Rasa Gesells. Biol. 2:663-672. 1905- 
** BATESON, W., SAUNDERS, E. R., and Punnett, R. C., Further experiments 
on inheritance in sweet peas and stocks: Preliminary account. Proc. Roy. 
London B. 77:2 236-238. 1905. 
22 See Bor. GazettE 40: sak: 1905. 
*3 See Bor. GazeTTE 40: 385. 1905. 
74 PEARSON, H. H. W., Some observations on abies mirabilis Hooker. 
Phil. Trans, Soc. London B. 198: 265-304. pls. 18-22. 19 
*S Bot. GazettE 41:226. 1906. 
