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May, 1909.] THE ORCHID REVIEW. 135 
ALBINISM IN DENDROBIUMS, 
THE facts underlying the production of albinos are sufficiently perplexing. 
It is now well known that albinos of distinct species or races, even if 
remaining constant when self-fertilised, frequently revert to coloured forms 
when intercrossed, but there are other cases where the union of coloured 
forms results in the production of albinos. One of the latter came before 
the Scientific Committee of the R.H.S. at the meeting held on April 6th. 
Flowers were sent from the collection of R. G. Thwaites, Esq., Streatham, 
which had been obtained from Dendrobium X Wiganiz and D. X Thwaitesiz 
crossed in both cases with D. xX Wiganiz xanthochilum, all the parents 
being yellow, but the hybrids in each case white, with a zone of purple on 
the disc of the lip. Mr. Thwaites wrote that six plants of the former had 
flowered, and three of the latter, all having similar features, and he added :— 
“You will notice that the pollen caps and flower pedicels are also white. 
I feel sure that it would be quite useless to use those flowers for obtaining 
white hybrids, and it may be that the unsuccessful attempts to obtain white 
flowers from apparently white parents is due to coloured parentage some- 
where behind the flowers used. Theseand other results, though apparently 
confusing, may later on assist in throwing light upon the albinism question, 
as notwithstanding the mass of contradictions which are appearing, [ feel 
sure there is some logical law relating to it.” 
Now D. X Wiganiz is ahybrid from D. nobile (purple with dark maroon 
disc to the lip) crossed with D. signatum (yellow), and has buff yellow 
flowers, with a dark brown disc to the lip, and D. X Thwaitesiz is a hybrid 
from D. X Wiganiz and D. X Ainsworthii (D. nobile <X D. aureum), the 
latter having light yellow flowers with a deep brown velvety disc. D. x 
Wiganiz xanthochilum is a brighter yellow form from the same capsule 
as D. X Wiganiz. Thus we can scarcely call the case before us one of 
reversion, but rather a problem as to how it is that in some cases the union 
of purple with yellow gives white. This often occurs when D. nobile is 
crossed with D. aureum, as witness the white forms of D. x Ainsworthii, 
but not when crossed with D. signatum, for we have no white forms of D. x 
Wiganiz ; yet in the cases now before us it cannot be due to the influence of 
D. aureum, for that species is not represented in D. X Wiganiz, and the 
albinism is equally pronounced in each case. The pollen parent was 
identical in each, but that does not help us to understand the phenomena. 
Nor does a Mendelian interpretation throw any light on the matter, for the 
first cross mentioned is simply the ‘‘ Fi’’ generation, to use the Mendelian 
notation, being simply the union of two seedlings out of the same capsule, 
and the albinism extends to all the six seedlings that have yet flowered. 
The “ cause ”’ of this curious behaviour is at present a mystery, but it would 
