TRANSACTIONS OF SECTION K. 565 



4. A Fifteen-year Study of Advancing Sand Dunes. 

 By Professor Henry C Cowles. 



My first observation of the dunes and dune vegetation of Lake Michigan was 

 at Dune Park, Indiana, in 1896. From then until the present time these dunes 

 have been under constant observation, and for most of this time also close study 

 has been made of advancing dunes at Furnessville, Indiana. Occasional trips have 

 been made to the gigantic advancing dunes at Glen Haven, Michigan. 



In the three districts studied the dunes are very high, the advancing front 

 having an altitude of twenty-five to sixty-five metres above the country in the 

 path of advance. So high are the dunes and so great is the rapidity of move- 

 ment that very few of the antecedent plants are able to survive. At Furnessville, 

 where the advance probably is relatively slow, exact measurements have been 

 made by marking the trunks of the trees upon which the dune is advancing ; the 

 horizontal advance here is one or two metres per annum. At Cape Cod, Massa- 

 chusetts, Nyssa sylvatica sometimes serves as a self-recorder of dune advance. 



Oddly enough the plants which are able to survive partial burial by dunes 

 are not Xerophytes (as the pines and oaks), but swamp plants and Mesophytes. 

 As previously described ('Botanical Gazette,' 1899), various species of Cornus, 

 Salix, and Populus often are able to survive a period of dune advance; the 

 shrubby species are stimulated thereby to extraordinary stem elongation. The 

 early assumption that survival depends upon the capacity of a plant to put forth 

 adventitious roots and to elongate as rapidly as the dune advances has been 

 shown to be correct. Such Mesophytes as Tilia americana and Ulmus americana 

 are quite as able to endure dune encroachment as are poplars and willows, and 

 for the same reasons. At Furnessville there are elms thirty metres in height 

 above the original country level; at the present time the tree-tops project only 

 one or two metres above the sand, but their foliage is healthy and they flower 

 and fruit vigorously. 



5. On the Brown Seaweeds of a Salt Marsh. By Miss Sarah M. Baker. 



The capability of giving rise to marsh forms seems to be shared by all the 

 brown seaweeds inhabiting the upper parts of rocky shores. Pelvetia canalicu- 

 lata, Fucus spiralis, Ascophyllum nodosum, and Fucus vesiculosus, all show 

 marsh varieties or species. The reason that Fucus serratus and F. ceranoides 

 have no representatives in the marsh habitat is probably their intolerance of 

 desiccation. 



The physical and chemical environment factors on the marsh being much 

 more complex and varied than on a rocky shore, one would expect a correspond- 

 ing variation in the structure of its plants. The most marked characteristics of 

 the common marsh species are a great tendency to spiral twisting or curling of 

 the thallus — and vegetative reproduction. That this latter feature is not directly 

 caused by the marsh habitat is shown by exceptional species where reproduction 

 is normal. 



The zoning of the brown seaweeds of a marsh is often very striking; but 

 the factors governing it must be far more complicated than those operating on 

 the seashore. 



The extensive mattings of brown seaweeds often found on English marshes 

 have a decidedly beneficial effect on the phanerogams. It seems possible that 

 F. volubilis may act as a pioneer in the establishment of salt marshes in certain 

 cases. 



6. The Causes of the Formation of Hairs and Palisade Cells in certain 

 Plants. By Professor K. H. Yapp, M.A. 



It has long been known that many plants have a marked power of responding 

 by structural changes to a varying environment. This is markedly true in 

 respect of the palisade tissue of leaves, and the hairs on aerial shoots. The 

 results of many previous observers and experimenters show that in general both 

 palisade cells and hairs tend to develop best under conditions which either 



