Eragrostis-Helianthus-xerasium: eragrostis-sunflower drainage succession Eragrostis-Polygonum-telmatium: eragrostis-heartsease wet meadow formation Helianthus-Ambrosia-chledium: sunflower-ragweed waste formation _INVESTIGATION OF SUCCESSION_ =328. General rules.= The study of succession must proceed along two fundamental lines of inquiry: it is necessary to investigate quantitatively the physical factors of the initial stages and the reactions produced by the subsequent stages. This should be done by automatic instruments for humidity, light, temperature, and wind, in order that a continuous record may be obtained. Water-content is taken daily or even less frequently, while soil properties, and physiographic factors, altitude, slope, surface, and exposure are determined once for all. It is equally needful to determine the development and structure of each stage with particular reference to the adjacent formations, to the stage that has just preceded, and the one that is to follow. For this, the use of the permanent quadrat is imperative, as the sequence and structure of the stages can be understood only by a minute study of the shifting and rearrangement of the individuals. Permanent migration circles are indispensable for tracing movement away from the pioneer areas by which each stage reaches its maximum. Denuded quadrats are a material aid in that they furnish important evidence with respect to migration and ecesis, By means of them, it is possible to determine the probable development of stages which reach back a decade or more into the past. In the examination of successions, since cause and effect are so intimately connected in each reaction, it is especially important that general and superficial observations upon structure and sequence be replaced by precise records, and that vague conjectures as to causes and reactions be supplanted by the accurate determination of the physical factors which underlie them. [Illustration: Fig. 70. Alternating gravel slides on Mounts Cameron and Palsgrove, from the comparison of which the initial development of the talus succession has been reconstructed.]