My guess would be that this description is referring to a pussy willow bush. The bush gets it's name because the catkins, or flower like portion of the plant, is as soft as a cat. The pussy willow, or Salix discolor, is found in the New England area where this story takes place. I have often seen it growing aside lakes and in lightly wooded areas just as the plant in the book is described. The story also describes a short bush which is very fitting to the pussy willow. This short plant does not usually grow above 6 meters. If you have ever held a pussy willow branch, it is covered in little gray-white balls that are fluffy and soft like cotton or animal fur. It is often used in decorating because of it's appealing touch and look.