TO BIRD’S-EYE FORMATION IN THE WooD OF TREES. 17 
bird’s-eye formation in wood is directly caused by the presence 
of numerous adventitious buds, and that bird’s-eye maple occurs 
principally where such buds have been formed in numbers, 
especially such as result from wounding. These buds are 
developed from small groups of meristematic cells produced by 
the cambium. Some develop into short-lived shoots, others 
persist as small woody cones. In either case they form 
cylindrical interruptions in the cambium, and the newly-formed 
elements of the wood and bast are forced to deviate from their 
usual course and form the characteristic convolutions round 
these centres or “eyes,” which can be always recognised in the 
net-work formed by the vasa. 
The late Professor R. Hartig? also proved that not only 
adventitious buds but also remaining pieces of old tissues, when 
they occur at a place over which callus is being formed, can offer 
the same local hindrance to the course of the newly-formed 
wood-elements, so that they become surrounded and isolated 
like islands in the callus. He observed in occlusions where the 
wood-body was covered with old bark still adhering to it by 
means of the medullary rays and remains of cortical tissue that the 
grain of the wood was interrupted by those remains, the newly- 
formed elements being forced to deviate round them. 
In anatomical structure the burred wood agrees in all essential 
points with normal wood, and Frank definitely states that it may 
be produced by a broadening of certain medullary rays with- 
out any accompanying adventitious buds or other foreign bodies, 
and he points out that, among former authors, Schacht alone 
mentions that burred wood can occur without any accompanying 
adventitious buds, and that the same author found very beautiful 
bird’s-eye formation on the outer year-rings of smooth stems of 
specimens of Adzes and Castanea which were several hundred 
years old. 
A curious case of burr-formation in the apple is mentioned by 
Sorauer?, who describes and figures certain groups of conical 
outgrowths, which may arise either on one side or all round the 
stem. Those groups occur principally at the base of the shoot 
*Hartig, Aeon goes des Holzes (1878), p. 136. Taf. XIX. 
Figs. 5 to 
*Sorauer, -Sehuts der Obstbaume (1900), p. 139- 
