This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Bog plants are perpetually exposed to wind, and are as a whole not tall. The development of the grass habit, in fact, establishes a more or less uniform height, which is from 9 in. to 1 ft. or 18 in. The necessity for adaptation to dry conditions also prevents upward growth.
The marsh flora containing tree types consists of much loftier types, and again, wind is less influential in a marsh than in an upland bog. The marsh flora is altogether less subject to dry conditions, hence the ground flora is more luxuriant, and the plants are generally more robust.