orr 
484 

Experimental Production of Green 
and Colourless Hydra. 
W GOETSCH, of Munich, has carried out a 
* series of experiments on Hydra, and has 
published the results in some half-dozen short papers, 
two of which form the subject of this notice (Die 
Naturwissenschaften, pp. 202-205, 867-871, 1922). 
Specimens of Hydra are either green, brown, or grey, 
and these are regarded by most authors as belonging 
to distinct species or even genera, though in certain 
cases the brown and grey are difficult to distinguish. 
Goetsch points out that the brown and green may 
also be difficult to distinguish, for some of the former 
can take green alge into their endoderm cells and 
form a symbiotic union similar to that long known 
in green Hydra. 
Goetsch obtained from a warmed tank in the 
Botanic Garden in Nymphenburg some brown Hydra 
which showed pathological features, and when he 
fed these with alge they developed a green colour 
first around the mouth, then in the foot region, and 
finally in the intervening portion, so that in about 
a fortnight the entire animal had an intense green 
colour. The spread of the alge was accompanied 
by a progressive diminution in the size of the Hydras 
so that they had difficulty in capturing their prey, 
the reserve material of the interstitial cells degener- 
ated, and budding ceased. These green examples 
disappeared from the aquarium, but a few which 
remained in culture vessels were fed with freshly 
killed Daphnia and were thus carried through their 
abnormal condition. The reciprocal toleration be- 
tween the Hydra and the alga soon becomes an 
intimate association. Afterwards these Hydra 
produced buds containing the green alge, and some 
of them showed ovaries or testes—apparently two 
were males and two were females. 
It is impossible to determine whether the specimens 
are H. attenuata or H. vulgaris. The alga in these 
green specimens is (as in the true green Chlorohydra) 
a Chlorella, but differs from that in Chlorohydra in 
being twice as large, and in being situated in the 
distal end of the endoderm cells, whereas in Chloro- 
hydra the alge are near the base of the endoderm 
cells. These green examples differ further from 
Chlorohydra in that the symbiosis is easily lost; if 
the green specimens are kept in the dark or cold 
the green colour disappears with the exception of a 
small amount around the base’ of the tentacles, 
but on transferring the specimens to better conditions 
the alge begin to multiply again. Specimens kept 
four weeks in darkness lost every trace of their 
alge ; the only way to make these green again was 
to introduce into them fresh alge contained in 
crushed pieces of green specimens enclosed in the 
carapace of a Daphnia. 
Goetsch suggests that this brown Hydra is a new 
mutant, and that with the origin of this mutant 
capable of receiving the alge in the warm house in 
the Botanic Garden the conditions were for the 
first time favourable for the institution of the sym- 
biosis. This union cannot be maintained through 
the cold of winter, and is not transmitted through 
the egg. In Nature the Hydras would probably not 
have come through the first attack by the alge, for 
those in the cultures owed their survival to artificial 
help. If a brown and a green specimen of the 
same species be cut into two and a brown piece 
and a green piece be joined together by means of a 
hair, there is a gradual extension of the alge into 
the previously uninfected part. 
The problem of the production of colourless 
specimens from the green Chlorohydra has also been 
No. 2788, VOL. 111] 
“NATURE 


[APRIL 7, 1923 
attacked by Goetsch. Colourless examples were 
obtained by Whitney by placing Chlorohydra in 
weak glycerine, which caused the endoderm cells to 
expel their alge. Hadzi kept Chlorohydra in the 
dark and they produced eggs without alge, and he 
thus obtained alga-free examples one of which was 
reared. Goetsch kept Chlorohydra under unfavourable 
conditions—cold, darkness, and lack of calcium—_ 
to suppress the growth of the alge, and then liberally 
fed the Hydra so that their cells multiplied so quickly 
that the alge could not keep pace. After a few weeks 
of such treatment the buds produced were of a paler 
colour, especially in the middle region of the body. 
As this is the region where asexual reproduction 
takes place, offspring were eventually obtained free 
from alge. These whitish specimens are more 
feeble than green examples, and require careful 
treatment. A spontaneous return of colour in these 
white specimens has not occurred, although some of 
them have lived for four months in the light. 
Deep green and colourless pieces were joined 
together and the spread of the green alge was studied. 
Alge thrust out of the endoderm cells of the green 
part are taken up with other food by the endoderm 
cells of the other part, so that after a few days the 
whitish part begins to exhibit a green colour, even 
at places distant from the junction. If a bud is 
formed at the junction of the two pieces it may be 
half green and half white. Such a bud affords 
oe evidence against the purely ectodermal origin 
of buds. 

University and Educational Intelligence. 
ABERDEEN.—At the spring graduation held on 
March 28, Sir George Adam Smith, the vice-chancellor, 
presiding, the degree of LL.D., honoris causa, was 
conferred on Sir William H. Beveridge, director of the 
London School of Economics; Dr. E. W. Hobson, 
Sadleirian professor of pure mathematics, University 
of Cambridge ; Dr. W. Mackie, of Elgin, distinguished 
by his researches on the geology of the north-east of 
Scotland; Sir George H. Makin, consulting surgeon to 
St. Thomas’s Hospital; and Prof. C. Niven, emeritus- 
professor of natural philosophy, University of Aber- 
deen. 
The degree of Doctor of Science (D.Sc.) has been 
conferred on Dr. J. L. Rosedale for a thesis—* On 
the Hydrolysis of the Proteins of Flesh.”’ 
The Senatus Academicus has appointed Prof. 
Matthew Hay to represent the University at the 
Pasteur centenary celebrations to be held in Paris 
and Strasbourg in May. 
Prof. Kruyt, Utrecht University, will deliver a 
university lecture in the faculty of science on May 11. 
DurHAM.—Prof. H. Louis, at present professor ot 
mining and surveying, and William Cochrane lecturer 
in metallurgy at Armstrong College, will vacate his 
appointments on September 30, 1923, on reaching 
the retiring age. Prof. G. Poole, of the University 
of Leeds, has been appointed as professor of mining. 
This appointment was made by the council on the 
recommendation of a joint committee of the College 
and the Durham and Northumberland Coal Trades 
Association. Dr. J. A. Smythe, at present senior 
lecturer in chemistry, will take over the William 
Cochrane lectureship in metallurgy ; other arrange- 
ments are being made in connexion with the survey- 
ing teaching, formerly under the supervision of Prof. 
Louis. 
Prof. R. F. A. Hoernlé, professor of philosophy, has 
now left England to take up his appointment as 
professor of philosophy in the University of Johannes- 
burg. The council of Armstrong College will proceed 

