PRESIDENTIAL ADDRESS. 561 



xerophytic nature of the foliage on the canopy of the trees under which it 

 grew. 



Here, too, we see the explanation of the striking difference between the micro- 

 phyllous and arborescent Calamites and Lepidodendracese, and the large ombro- 

 phile foliage of the Filicineae and Pteridosperms, which spread out their shade- 

 leaves under the cover of marsh xerophytes, inexactly the same way as Professor 

 Yapp has so admirably depicted for recent plants in his account of the ' Strati- 

 fication in the Vegetation of a Marsh.' 



The development of a mesophytic vegetation in the shelter of the marsh 

 xerophytes makes it unnecessary to postulate an obscuration of the intense sun- 

 light by vapours, as was done by Unger and Saporta for the Carboniferous period. 

 The assumption of a variety of conditions of plant life within the same area helps 

 materially to clear up the difficulties presented by the somewhat incongruous 

 occurrences met with in the petrified plant-remains. The presence of fragments 

 of Cordaites, mixed with those of Calamites and Lepidodendra, in the coal-balls 

 cannot always be explained either by a drift theory or by conceiving the frag- 

 ments to be wind-borne ; but, given an area of retrogressive peat above the ordi- 

 nary water-level, and even so xerophytic a plant as Cordaites might well establish 

 itself there, its mycorhiza- containing roots being well adapted for growth in 

 drier peat. The curious occurrence of more or less concentric rings in the 

 secondary wood of the stem and roots of Cordaites may represent a response, 

 probably not to annual variations of climate but to abnormal periods of drought, 

 which would affect the upper-peat layers, but not the water-logged soil in which 

 were rooted the Calamites and Lepidodendra. 



If, as I suspect, we had in the peat deposit of the coal-seam a succession of 

 associations, we ought to find its growth and history recorded by the sequence 

 of the plant-remains, very much as Mr. Lewis has discovered with such signal 

 success in our Scottish peat-bogs. That some differences occur in the plant- 

 remains building up a seam can be noted by a microscopic examination of the 

 coal itself, in which, as Mr. Lomax tells me, the spores of Lepidodendra occur in 

 definite bands. But no systematic attempt has as yet been made to investigate 

 from this point of view the seams charged with petrified plant debris. Before 

 the Shore pit, which was reopened last summer through the renewed generosity 

 of Mr. Sutcliffe, was finally closed down, I obtained two series of nodules, 

 ranging from the floor to the roof of the seam, and have had these cut for 

 detailed examination. I should not, however, like to make any generalisation 

 from these isolated series, but intend, during the coming winter, to investigate 

 in the same manner further series taken from large blocks of nodules, which 

 have been removed bodily so as to retain the position they occupied in the 

 seam. Though at present the data are only fragmentary, there seems to be some 

 indication that the plant-remains are not without some relation to their position 

 in the seam. Of course, Stigmarian rootlets are ubiquitous, and in the nodules 

 of the lower part of the seam predominant, but other plant-remains appear to be 

 more frequently found at one level of the seam than another. The problem, 

 however, is very involved, and it has become apparent that it is as important 

 to study the fine debris in which the larger fragments are embedded as the 

 distribution of these latter. Moreover, attention must be paid to the stage of 

 decomposition presented by the particles forming the matrix of the nodule, as 

 this varies in the lower and upper parts of a seam, very much as in a peat-bed 

 we can distinguish the lighter-coloured fibrous peat from the darker layers at 

 the base of a peat-cutting. Mr. Lomax, who has so unique an experience of 

 these coal-balls, informs me that he can tell whether a nodule is from the top or 

 bottom of the seam by the lighter or darker colour of the matrix. The import- 

 ance of applying the methods which have been so successful in elucidating the 

 history of modern peat-deposits to the investigation of the coal-seam will be 

 clearly appreciated both by palaeobotanists and ecologists, and this particular 

 problem offers a striking illustration of the interdependence of various branches 

 of botanical investigation. It is fortunate indeed that the two fields of work, 

 Paleobotany and Plant Ecology, though they have been subjected to fairly inten- 

 sive cultivation, have not become exclusively the domain of specialists. The 

 strength and progress of modern Botany have been due to the close collaboration 

 of workers engaged in different branches of botanical science, and the fact that 



1911. 



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