STRUCTURE AND HISTORY OF PLAY. 237 
The Danube and the Balta in Rumania. 
The river Danube is subject throughout almost its entire length to floods, 
which occur two or three times in the year. These floods are perhaps its 
most striking natural feature, and leave, in the vicinity of the river, a general 
impress upon organic nature. They vary in height and duration and, what 
is of greater importance as regards static biological conditions, they regularly 
vary at different places along the river-course ; theoretically, therefore, a 
very great number of variations in the assemblage of animals and plants, in 
their mode of assemblage, and in their less obvious habits of life, are to be 
looked for along the Danube, and thus any given spot along the river is 
likely to exemplify a more or less definite organic entity. The Danube 
floods in Rumania will, however, for the purpose of this paper, only be 
considered where the river runs its final course and enters the tideless * 
Black Sea, and their significance there only in so far as they concern Plav, 
the subject of this paper. 
The floods of the Danube occur in Rumania usually three times in the 
year. They follow, first, on the autumn rains, second, on the breaking 
up of the ice, and third, on the spring rains, and more especially on the 
coincident event of the melting of the snows of the Danube watershed as a 
whole. 
The autumn floods are, for the most part, slight, seldom rising above the 
river-banks. The floods due to the breaking up of the ice are often con- 
siderable in magnitude, but of less regular and more local occurrence than 
either autumn or spring floods. They are often caused by dissimilai 
temperature conditions in the upper and lower courses of the river, whereby 
the ice breaks up earlier above than below, with the result that the ice in 
the lower portion of the river forms a barrier to the waters collected above. 
The spring floods are by far the largest, and prevail from March to the end 
of June, and sometimes even from February into August. 
Records of the height and duration of the floods in Rumania have been 
kept at different places along the river-course by the European Commission 1 
and by the Rumanian Hydrographic Service, in some cases for as long a 
period as thirty consecutive years. These records show that the floods differ 
in height at different points. Thus at Turnu Severin, which is close to the 
Rumanian frontier and 931 kilometres (about 5784 miles) from the port of 
* According to Sir Charles Hartley the sea falls some 18 inches (about 45-7 cm.) below 
its mean level with violent westerly winds, and with strong easterly winds rises about 
2 feet (about 0'6 m.). 
See Hartley, Sir Charles А., “ Description of the Delta of the Danube, and of the Works 
recently executed at the Sulina Mouth," Minutes of Proceedings of the Institution of Civil 
Engineers, vol. xxi. Session 1861-1862. 
* See article ^ Danube " in the Encycl. Brit. 
