88 THE AMERICAN BOTANIST 



chance to grow. Such species are the hedge-mustard, (Sisyntr- 

 brium officinale var. Iciocarpuni), lamb's quarters, (Chenopo- 

 dium album), pigweed, (Aiiiaranthus albus), and some other 

 common weeds. Then birds find the tree a convenient place to 

 roost, and bring in the seeds of many other plants, such as 

 pokeberry, Virginian creeper, Japanese ivy. mulberry and 

 nightshade. Most numerous of all, however, are the seed- 

 lings of trees with winged seeds, including the elm, box elder 

 and green ash. These seeds are blown in by the wind from 

 trees near by. In all about twenty-five kinds of plants are 

 found beneath the tree in an area of not more than three hun- 

 dred square feet. 



Another Growth-ring. — In a preceding issue a number 

 of different forms of growth rings were mentioned. A more 

 peculiar one has been common this summer in meadows and 

 pastures, formed, by the slime-mould Physarum cinereum 

 Slime moulds are small simple organisms, sometimes con- 

 sidered to be fungi and sometimes regarded as animals. The 

 plant body is a slimy mass of naked protoplasm, which has a 

 slight power of locomotion. When it is ready for reproduct- 

 ion, it creeps up the stems and blades of the grass where it is 

 living and develops conspicuous gray powdery masses of 

 spores. Gray rings, where the grass is covered with the 

 spores, have been common this summer, probably because the 

 frequent rains have been favorable for the growth of the slime- 

 mould. The largest of them are six to eight feet in diameter. 

 No adequate reason has been given as to why these plants live 

 in rings. 



Other Plants in Strange Places. — The ecologist be- 

 lieves that if the external conditions are right for a plant, in 

 any place, and if the plant has adequate means for migration, 

 the plant will sooner or later be found there. Many years ago 

 a railroad crossed a deep valley by following a ravine from the 



