No. 422.] PHYLLOSPADIX AS A BEACH-BUILDER 107 
as the parent stem creeps on it leaves on either side of its trail 
a series of new rhizomes, starting out at right angles to the old 
one. In like manner this new generation of rhizomes branch 
and rebranch, growing over and upon one another, till, in a few 
years, the bowlders, as well as the bed-rock, are covered bya 
patch of eelgrass, — a thick mattress, which, as it lies in sinu- 
ous tangles at low tide, quite dissipates the force of a hammer, 
though swung with all the energy of an enthusiastic botanist, 
and so must, one would think, considerably lessen the effect of 
the forces which are ordinarily at work reducing the bowlders 
to pebbles and grinding down the rock itself. 
This brings us to the second phase of our subject, namely, 
the significance of such a plant as Phyllospadix to the geolo- 
gist. What we wish to show is that under some conditions 
the effects of the plant in modifying the results of wave and 
current action are worthy of consideration. 
Various geological authorities have commented upon the 
protection afforded to shore rocks by some marine plants, and 
upon the accumulation of detritus by others. Certainly no 
plant is better adapted to either of these functions than Phyllo- 
spadix. In the first place its manner of growth is exceptional, 
resulting, as it does, in the formation of a broad, continuous 
patch, instead of a scattering of individuals. Again, unlike the 
soft or rubbery fronds of the algz, its leaves are strengthened 
by extremely tough bands of collenchyma fibers. : 
A moment ago we noticed how the eelgrass bed, the growth 
of which from a seedling we have sketched, covers the bowlders 
with a thick mattress which must prevent attrition between 
the loose stones and pebbles. At Bodega Bay may be seen 
such a bed, where, at low tide, one may stumble for rods along 
a bowlder-strewn shore without seeing the rock under foot, all 
being overlaid by the tangled mat of eelgrass. Now, it might 
be objected that the corrosive action of the acids excreted by 
root-hairs would offset the protection the plant might afford 
to the rock. But it is at once obvious that the root-hairs of 
Phyllospadix are, in this respect, unlike those of most plants. 
Their essential function is that of attachment, not patrition, 
and, of course, if they should cut the gr ound from under their 
