OF A CAMBRIDGESHIRE WOODLAND, 373 
This society passes gradually into the Fragaria vesca Society on the 
saleareous clay at the point where the two soils unite. Angelica sylvestris and 
Orchis mascula are extremely abundant in the transition zone. This part is 
of varying extent and marked by a mixture of species from the two sides; 
Holeus mollis occurs but is not abundant, Myosotis umbrosa and Careg sylvatica 
are abundant. Many of the species do not enter this region at all; thus Primula 
elatior and Viola sylvestris are confined to the clay side, and Luzula sp. and 
Carer pilulifera to the loam sido. 
Periodie Changes in the Plant Societies, 
A fairly marked periodic change can be made out in some of the societies, 
especially on the calcareous clay, governed by the periodic cutting and 
regrowth of the shrebs. For example, the shade type of the Spiræa Ulmaria 
Society may be looked on as a final shade phase. When the shrubs are cut, 
light and evaporation are suddenly increased. The general result is that 
numerous outside species enter, and also that the vernal herbs, especially 
Primula elatior, Ajuga reptans, Nepeta hederacea, and Carer sylvatica, suddenly 
increase in quantity and luxuriance. Numerous species that were quite 
subsidiary in the shade become prominent, especially Angelica sylvestris, Geum 
urbanum, Epilobium spp., and Centaurium umbellatum. The Spirwa at this 
time gets forced into local pure patches amongst the mixed vegetation. 
Also, as mentioned above, grasses, especially Deschampsia cespitosa, come in 
and grow very rapidly ; Rubus eeosius also is an early invader by means of 
its long and rapidly growing trailing shoots. 
For the first two or three years the ground flora is very mixed, but as soon 
as the shade begins to be reformed many of the species become enfeebled and 
are crowded out by more tolerant forms. As a general rule, the Spirwa 
Ulmaria-Deschampsia cuspitosa Society, or one of its sub-societies, becomes 
established about the fourth year. Then, by the gradual increase in shade, the 
Spirea Стата increases at the expense of the others, as 16 is more tolerant 
and plastic. Deschampsia cæspitosa is very intolerant of deep shade, and even 
in the shady parts of the Spirea Ülmarta- Deschampsia: eespitosa Society it 
does not flower much. Thus by the gradual elimination of sun-plants and 
intolerant species the shade phase is again reached. 
Similar transitions can be followed in the Mercurialis perennis Society. In 
this after cutting Rubus estis tends to overrun the area for а time. 
GENERAL NOTES ON THE FLORA OF THE Woop. 
A complete list of plants found growing in the wood is given as an 
appendix, The number of aliens it contains is due partly to the cutting, 
when many plants obtain a temporary footing, and partly to the materials— 
grain, straw, &e.—brought in in connection with the rearing of pheasants and 
to invasions along drives and paths. 
