76 THE SALTON SEA. 



wherever a portal of entry to the tissues of cortex, phloem, and cambium had been pro- 

 vided. On the contrary, the specimens whose ends had been protected by paraffine caps 

 possessed a firm, close cortex and phloem which adhered as tightly to the woody cylinder 

 five months after the cultures were made as when the specimens were first immersed. 



The various stages of progressing decortication are indicated in Plates 13 and 14. In 

 the latter stages the effects of decortication are pronounced, notably in Larrea tridentata 

 (Plate 14, p, Q, o.) Moreover, it is evident that wherever the branches had sharp and even 

 sections (Plate 13, b, c, g, h, i, and Plate 14, transverse sections of n, o, p, q), the progress 

 of decortication was far less rapid than in those branches which were broken at an angle 

 producing ragged, jagged fractures, which furnished an admirable portal of entry to any 

 bacterial organisms present in the culture. (Plates 13, d and e, and 14, N, o, p, and Q.) 



In order to make microscopical investigations of the changes in the immersed speci- 

 mens, sections of the various woods were prepared. Different methods of technique were 

 employed, but the most successful results were secured when specimens of wood were 

 softened for three weeks in hydrofluoric acid, thoroughly washed and imbedded in gelatine, 

 hardened in formaline, and sectioned in a swinging microtome, stained 36 hours with 

 safranine followed by a very brief treatment with aniline blue. Studies of these woods 

 showed that the tissues of the woody cylinder were unchanged, likewise the lignified re- 

 gions in the phloem were unaltered. (Plate 13, f and k, and Plate 14, e.) A distinctly 

 different condition was present in unlignified parenchyma zones which alternated with the 

 lignified zone in the phloem ; and a notably disintegrated state of affairs was found in the 

 region of the cambium. The walls of the meristem were totally dissolved in places and 

 disintegration following the hydrolysis of these delicate walls had progressed so far that 

 the slightest disturbance caused a breaking away of the whole cambial region from the 

 woody cylinder, marking, of coiu"se, a completion of the decorticating process (Plate 13, 

 D and E, and Plate 14, p, q, and o). The two factors entering into this lack of uniform 

 decortication are the number of layers of cambial cells intervening between the phloem 

 and xylem and the degree of accessibility afforded to the agents which might act upon the 

 walls of the cambial cells. This, in a measure, would explain why some trees, submerged 

 for five years in the Salton Sea, were found to have patches of cortex remaining after they 

 were exposed by the lowering of the water level. 



The breaking down of the walls in the zone of the cambium and in the meristematic 

 regions of the unhgnified zones in the phloem (see Plate 13, d and e, and Plate 14, p and q), 

 can not be accounted for merely by reason of their having more delicate structure than 

 that which characterizes the cells in the woody cylinder and in the lignified zones of the 

 phloem. It is true that it would be possible to rend delicate tissues of this character if 

 considerable physical force were applied to external parts of the uninjured specimens. 

 Such an explanation, however, does not fit this case of decortication. There is a difference 

 not only in the strength of the cell walls in these different regions, but there is a difference 

 in the chemical composition of the walls of the cells of the cambium, the woody cylinder, 

 and the lignified regions of the phloem. This was set forth by Mangin' who held that the 

 cellular membrane in young tissues differed from that in adult tissues. He definitely 

 denied that cell walls were composed of pure cellulose. He affirmed that they were always 

 associated with groups of pectins which are essentially distinguishable by color reactions 

 and by certain optical properties, and by great mutabiUty under the action of acids and 

 bases. After conducting extended researches, he concluded that tissues might have their 

 cell walls disa-ssociated by four different processes: (1) prolonged boiling in pure water; 

 (2) prolonged boiling in a 2 to 5 per cent solution of caustic soda or caustic potash; (3) 

 continued action in a cold, weak acid and solvents of pectic acid, alkalines, alkaline salts, 

 ammonia water, and organic acids; and (4) it was possible that certain organisms, which 



1 Man^: Jour, de Bot., vol. vii, p. 336, 1893. 



