ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
813 
activity of the cambium is diminished. The former is generally the 
case in the spring, the latter in the summer. The lowest branches of 
a tree and the lowest parts of a branch are those in which the activity 
of the cambium continues the longest ; and these are therefore the regions 
in which the annual layers are the moot developed. Broad layers with 
large thin-walled cells may, however, acquire great density from the 
walls becoming strongly impregnated with tannin or resin. 
Influence of Annular Decortication on Trees.* — M. E. Mer has 
studied the effect produced on a variety of trees by the removal of a ring of 
bark ; the result varies greatly according to a variety of circumstances. 
As a general law it may be stated, that when the decortication is per- 
formed in May, the branches formed subsequently in the region abovo 
the decortication are less vigorous, the foliage is paler, and a number 
of the buds remain dormant. In the region below the ring, on the 
other hand, no such deteriorating effect is at first produced ; but, on the 
contrary, the leaves are larger and of a deeper green, and the growth of 
the branches is more rapid ; the nitrogenous materials obtained from 
the soil become concentrated, owing to their not being able to pass the 
decorticated a ring. But when the supply of starch in these parts is 
once exhausted, it is not again renewed. From this it follows that it 
is through the bark that the downward flow of food-material takes place, 
and the decortication puts a stop to this descent. The formation of 
cambium is, therefore, arrested, even in the region below the decortica- 
tion ; and the development of fresh rootlets also ceases. 
Formation of Thyllae in the Tracheids of Conifers.f — Herr W. Baatz 
has investigated the mode of formation of thyllre in the wood of conifers, 
especially Pinus excelsa. They are frequently septated, and sometimes 
branch to such an extent that the original position of the cell can no 
longer be made out. When fully formed they have simple pits on all 
sides, including those which impinge on the walls of the tracheids. 
Similar thyllae were found also in Abies pectinata, Pinus sylvestris, P. 
Strobus , Picea excelsa , Larix europsea , and Thuja occidentalis. They are 
much more numerous in the root than in the stem. The function of the 
thyllae is evidently connected with the healing of wounds ; they close 
up injured vessels (tracheids) in the same way as does an exudation of resin 
or gum. They are formed at the same time as the new jmrenchyme 
which closes the wound. It is very rarely that they are found inde- 
pendent of an injury. In the winter they contain abundance of starch, 
and serve as a reservoir for food-material. 
Cystoliths.J — According to M. L. Mangin, the matrix of cystoliths 
consists, in addition to cellulose, of pectic substances, and very frequently 
also of callose. The presence of the latter substance was shown by 
treating thin sections with a mixture of extra 6 B soluble blue and 
vesuvian brown or orcellin B B, which gives a characteristic blue colour 
with callose. Callose was detected in this way in the membranes or 
calcareous incrustations in a number of Urticaceae, and in the hairs on 
* Bull. Soc. Bot. France, xxxix. (1892) pp. 107-20. 
t Ber. Deutsch. Bot. Gesell., x. (1892) pp. 183-92 (1 pi.). 
X Comptes Rendue, cxv. (1892) pp. 260-2. 
