E 
1899] Robinson, — Fairy-rings formed by Lycopodium 29 
reduced scale, the position of the stems in a ring, a mechanical device 
was found useful. This consisted of four laths of equal length, fastened 
together at the ends so as to form a square, which was then strung 
with numerous cords running at equal, carefully measured intervals and 
crossing each other at right angles. This network, when laid over a 
ring, gave at once a sort of latitude and longitude by which the posi- 
tion of the different parts could be told very readily. 
Slight examination showed that the rings develop in the most 
natural way. A young plant, starting from a centre, sends out its 
prostrate forking stems in all directions, until soon a small patch of 
ground is pretty uniformly covered with the stems. These areas, al- 
though subject to irregularity from obstructions, are usually about 
circular. Several were observed which were from 2.5 dm. to 4 dm. 
in diameter. Now, it is a well-known fact that the prostrate stems of 
Lycopodium inundatum as they grow, constantly root near the tip, 
while the older parts begin to die and decompose. Anyone who has 
collected the species will recollect that his specimens, no matter how 
carefully selected and dug, are pretty sure to consist only of a single 
short, slightly branched stem, fresh and green at one end, but yellow 
and decayed at the other. "With this mode of growth and the early 
tendency of the stems to develop radially or centrifugally, the formation 
of the rings is at once explained. The older parts of the plant, which 
are at the centre, are the first to die away, and what is left is a ring of 
separate, diverging branches of what was once a single plant. "These 
continue to grow as independent individuals. 
As the branches grow outwards at their vegetative tips, their inner, 
older ends gradually die and so the rings get larger year by year. The 
size of the ring is thus an approximate indication of the age of any 
particular colony. The stems appear to grow from 2 to 3.5 dm. in 
one season; a ring would, therefore, add nearly a foot to its radius 
each year, and its age be roughly found by halving its diameter ex- 
pressed in feet. 
It is not maintained that the rings are always so períect as our 
theory would make them. There are several obvious sources of irreg- 
ularity. The chief of these are the crowding of other plants, inequal- 
ities of the ground and especially the fact that neighboring rings often 
become confluent and confused. In several cases reéntrant bands of 
stems were observed, which seemed again developing into the hollow 
of the ring. However, making all due allowance for irregularities, the 
