QUADRATS 173 
or year, the tapes are placed with reference to the stakes, and a chart and 
photograph are made in the usual manner. These are labeled and dated like 
the original ones, but they are numbered to indicate both the quadrat and the 
series, e. g., 15? indicates the second chart, and photograph made of quadrat , 
15. The date indicates whether the readings are by the aspect or the year, 
though this may be shown also in the name of the series itself. It is clearly 
an advantage to have the two successive charts of a quadrat upon the same 
sheet, and to file all the charts and photographs of the same permanent quad- 
tat together, and in the proper order. 
Since much of the value of a permanent quadrat depends upon its use as a 
station for observing physical factors, it is unprofitable to establish a large 
number. The results of invasion and competition can be ascertained by the 
quadrat alone, but these should be merely preliminary to seeking for their 
causes. Clearly, a quadrat should ‘be established for each battery of instru- 
ments, while additional ones should be located only in so far as they can be 
visited often enough to give an insight into the factors that control them. 
Tn view cf the fact that the most important factors, water-content and light, 
are less variable than humidity, temperature, and wind, it will suffice if visits 
are made once a week. This is especially true when it is possible to refer 
the more variable factors to the continuous records of a base station. While 
all the results determined for permanent quadrats are preserved in the field 
record, a record of them is also kept on the reverse of the chart sheet for 
convenience in interpreting the different charts. 
The Denuded Quadrat 
213. Description. This is primarily a permanent quadrat from which the 
plant covering has been removed, after it has been charted and photographed. 
What is practically the same thing is obtained by establishing a permanent 
quadrat in a new soil, or in one recently laid bare and not yet reclothed with 
plants. These, however, are merely permanent quadrats, in which the first 
chart and photograph furnish a record of the habitat alone. They are of 
great importance in succession, and will be more fully discussed under ex- 
perimental vegetation. The denuded quadrat is of the usual size, 1 meter, 
though the smaller lichen quadrats are also denuded. The location is sub- 
ject to the conditions already indicated, especially with reference to physical 
factors. The denuded quadrat, however, is particularly adapted to the study 
of invasion and the resulting competition. Consequently, when migration is 
markedly from one direction, a series of denuded quadrats throws a flood of 
light upon the actual steps in invasion. Denuding is a valuable aid in suc- 
cession, but it must be clearly recognized that, while permanent quadrats 
