834 DR R. K1DST0N AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
the atmosphere, or of the presence in this of injurious vapours. Numerous examples 
of such intumescences are given in works on plant-pathology.* Perhaps the most 
striking figures for comparison are the photographs of intumescences t formed 
beneath the open stomata of leaves of cauliflower, etc., as a result of the entry of 
dilute vapour of ammonia. The elongation of the affected cells at right angles 
to the surface, and their subdivision by thin walls in the intumescences, present a 
remarkable similarity to the changes which result in the hemispherical projections 
of Rliynia. 
There are no close comparisons to advance for the production of definite organs 
as new growths from intumescences. The tissue composing the latter does not, 
however, differ profoundly from callus, which, as is well known, is often the seat of 
adventitious growths. 
hi connection with the hemispherical projections and adventitious branches of 
the stems of Rliynia Gwynne-Vaughani another feature which is clearly patho- 
logical must be briefly described. A considerable number of the stems show dark 
necrosed areas extending more or less deeply from the epidermis ; in other 
specimens the dark necrosed mass is wanting or has more or less completely 
disappeared leaving a larger or smaller cavity. Examples of these appearances are 
shown in figs. 11-14. In some cases the necrosed area appears to be related to the 
place of detachment of an adventitious branch (Part I, fig. 55), and sometimes it 
corresponds to the position of a hemispherical projection. Often, however, no such 
relation is to be traced. The necrosis cannot be proved to be related to the position 
of a stoma, though this possibility is by no means excluded. There is no evidence 
that the necrosis is caused by the presence of fungi ; fungal invasion may be 
extensive without any signs of necrosis. Fungal filaments and other organisms 
may, of course, be present in the resulting cavities. 
The feature of special interest is the behaviour of the cells abutting on the 
necrosed area or bounding the cavity. As shown in figs. 12-16, they had undergone 
changes that must have taken place during the life of the tissues. The cells are 
often elongated at right angles to the dead tissue of the cavity, and frequently show 
evidence, by the presence of thin walls, of an active cell-division that can without 
doubt be interpreted as a reaction to the wound. The arrangement of the cells and 
the mode of growth of the tissue resembles what is found in the formation of the 
hemispherical projections. 
The further interest of these peculiarities of the remains of Rliynia Gwynne- 
Vaughani will be considered in the section of Part V dealing with the conditions of 
accumulation and preservation of the deposit. 
* Of. Sorauer, PJlanzenkranldieiten, Aufl. 3, Bd. 1, p. 435 ff. Kuster, Pathologische Pflanzenanatomie, 
Aufl. 2, p. 44 ff. 
f Erwin F. Smith, “Mechanism of Tumor Growth in Crown Gall,” Jour. Agric. Res. ( Washington ), vol. viii, 
pi. 60 , etc. 
