STRUCTURE AND HISTORY OF PLAY. 269 
gradation in age would à priori appear probable. On the other hand, if 
the single thicket be assumed to be the major unit, it is necessary to explain 
how the different thickets have become joined together—how did they come 
to be so closely welded? Though I can make no assertion, it seems to me 
possible that the accompanying plants could effect such a union. 
If the single thicket be assumed to be the major unit, its area as 50 squared 
metres (— 2500 square metres) and the annual output of leafy shoots as 
15 lbs. (6:80 kilog.) per 4 square metres (43 square feet), then the total 
annual output of aerial parts 13 9375 lbs. (4252 kilog.), and if the annual 
output of rhizome also be taken as 15 lbs. (see p. 257), the total output of 
reed per year is 18,750 lbs. (8504 kilog.). ‘Then, with a length of life of 
100 years (probably аз а rule а low figure *), the mass of the reed-thicket 
(green) is about 837 tons (850,400 kilog.). If, on the other hand, a whole 
Plav be assumed to be the major individual, the figures would be about 
three times as great, i.e., 2511 tons (2,551,200 kilog.). These figures 
naturally represent the minimum mass, since there is no proof that the reed 
is not able to form a very much larger mass if divided. The figures must 
rather be taken as eomparable to the mass of a tree which cannot be 
multiplied somatically. 
So far I have no figures regarding the length of lite of a reed-thicket, nor 
have I a reliable notion of the initial annual horizontal inerement of the reed, 
both of which would be of some help in arriving at an approximation of its 
mass, though, as explained in the introduction to Part II., I regard both these 
figures as variables within wide limits (see p. 253). 
The Reed and its Competitor Typha. 
One plant, Typha, competes successfully with the reed (in the delta of the 
Danube it is Typha angustata, Bory & Chaub., and in the Norfolk Broads 
T. angustifolia, Linn.), though I do not think that it ever supplants the reed 
absolutely, but merely inhibits its growth for a time. 
In the delta, Phragmites invades deeper water than Typha, hence it is 
only in shallow water, or in water whose depth has been reduced by the reed- 
rhizome, that Typha and Phragmites enter into competition. Thus Typha 
often settles on the reed-rhizomes, and then, together with the reed, builds 
up one Plav, in which case, if judged by the aerial parts, Typha appears to 
be the dominant plant, for the reed sends very few shoots to the surface. If, 
however, the Plav is sectioned, it will be found to consist of living reed- 
* On the assumption that equal areas are covered by the reed each year, its radial 
advance will decrease (see p. 257). With a circle of 25 yards (22:86 metres) radius, there- 
fore, and allowing 100 years for that radial advance, the radius of the initial circle is 
73 feet (728 metres)—-too great a figure judging from the size of the reed-patches I saw on 
Lake Мегре! (see р. 256); hence the length of life of the major unit of the reed would 
appear to be greater than 100 years. 
