TRACES OF WOOD-BORERS IN PETRIFIED TISSUE.
There is one other form of pitfall which should be briefly noticed. In sections of petrified plants one occasionally finds clean cut canals penetrating a mass of tissue, and differing in their manner of occurrence and in their somewhat larger size from ordinary secretory ducts. Such tunnels or canals are probably the work of a wood-boring animal. An example is illustrated in fig. 24 A. Similarly it is not unusual to meet with groups or nests of spherical or elliptical bodies lying among plant tissues, and having the appearance of spores. Such spore-like bodies appear on close examination to be made up of finely comminuted particles of tissue, and in all probability they are the coprolites of some xylophagous animal. Examples of such coprolites are shown in fig. 24 A[154], and in fig. 24 B an interesting manner of occurrence of these misleading bodies is represented. The framework of cells enclosing the nest of coprolites in fig. 24 B, represents the outer tissues of a Lepidodendroid or a Sigillarian leaf; the inner tissues have been destroyed and the cavity is now occupied by what may possibly be the excreta of the wood-eating animal.
Some of the oval spore-like structures met with in plant tissues may, as Renault has suggested, be the eggs of an Arthropod[155]. In a section of a calcareous Coal-Measure nodule in the Williamson collection (British Museum)[156] there occur several fungal spores or possibly oogonia lying among imperfectly preserved Stigmarian appendages. Associated with these are numerous dark coloured and larger bodies consisting of a cavity bounded by a simple membrane; the larger bodies may well be the eggs of some Arthropod or other animal.
PHOTOGRAPHY AND ILLUSTRATION.
In looking through the collections of Coal-Measure plants in the Museums of Berlin, Vienna and other continental towns, one cannot fail to be struck with the larger size of many of the specimens as compared with those usually seen in English Museums. The facilities afforded in the State Collieries of Germany to the scientific investigator may account in part at least for the better specimens which he is able to obtain. It would no doubt be a great gain to our collections of Coal-Measure plants if arrangements could be made in some collieries for the preservation of the finer specimens met with in the working of the seams, instead of breaking up the slabs of shale and consigning everything to the waste heaps. There is one more point which should be alluded to in connection with possible sources of error, and that is the essential importance of accuracy in the illustration of specimens, especially as regard type-specimens. It is often impossible to inspect the original fossils which have served as types, and it is of the utmost importance that the published figures should be as faithful as possible. M. Crépin[157] of Brussels, in an article on the use of photography in illustrating, has given some examples of the confusion and mistakes caused by imperfect drawings. It does not require a long experience of palaeobotanical work to demonstrate the need of care in the execution of drawings for reproduction.
CHAPTER VI.
NOMENCLATURE.
“I do not think more credit is due to a man for defining a species, than to a carpenter for making a box.”
Charles Darwin, Life and Letters, Vol. I., p. 371.
Any attempt to discuss at length the difficult and thorny question of nomenclature would be entirely out of place in an elementary book on fossil plants, but there are certain important points to which it may be well to draw attention. When a student enters the field of independent research, he is usually but imperfectly acquainted with the principles of nomenclature which should be followed in palaeontological work. After losing himself in a maze of endless synonyms and confused terminology, he recognises the desirability of adopting some definite and consistent plan in his method of naming genera and species. It is extremely probable that whatever system is made use of, it will be called in question by some critics as not being in strict conformity with accepted rules. The opportunities for criticism in matters relating to nomenclature are particularly numerous, and the critic who may be but imperfectly familiar with the subject-matter of a scientific work is not slow to avail himself of some supposed eccentricity on the part of the author in the manner of terminology. The true value of work may be obscured by laying too much emphasis on the imperfections of a somewhat heterodox nomenclature. On the other hand good systematic work is often seriously spoilt by a want of attention to generally accepted rules in naming and defining species. It is essential that those who take up systematic research should pay attention to the necessary though secondary question of technical description.