1906] CURRENT LITERATURE 73 
The second part of the book is devoted to descriptions of special diseases. 
These are classified according to the nature of the crops on which they occur, 
as follows: Timber and shade trees; Field and forage crops; Garden net 
Orchards and vineyards; Greenhouse and ornamental plants; Wild pla 
Under those heads the groups of fungi, as rusts, smuts, mildews, etc., are 
together —H. HaAssELBRING. 
Regeneration. 
WITH THE TITLE Studies in regeneration NEMEC? has published in rather 
voluminous form the results of his investigations on the regeneration of root-tips. 
The general conclusions may be briefly summarized as follows. Cutting a trans- 
verse section just at the tip results in the regeneration of a new tip in a radial 
manner. The dermatogen-and outer part of the periblem takes no part in this, 
the new tissue arising from the inner part of the cortex and the plerome. There 
is first of all the formation of a callus of hypertrophied cells, between which and 
the meristem arises the group of initials by which the new root-tip is organized. 
This group is radial from the beginning, the majority of its cells arising from the 
plerome, only the peripheral ones coming from the periblem. Proceeding back 
from the tip, the se tesane for regeneration diminishes from the periphery inwards, 
soon disappearing from the periblem. As long as the central cells of the plerome 
still possess this capacity the regeneration is radial. Farther back it is confined 
arises. When the capacity of the inner cells of the periblem and the outer cells 
of the plerome to take part in regeneration is lost, the replacement of the removed 
root-tip occurs only through the origin of lateral roots, which arise in the peri- 
cambium. 
When the root is cut through obliquely, the regeneration of the new root-tip 
occurs at the part of the cut surface nearest the tip. When the tip is slit lengthwise 
each half re-forms a new tip. If a tip is slit lengthwise for about 1™™, and then 
one of the halves is removed by a transverse incision, the remaining half regene- 
rates a new half, and also, at the surface formed by the transverse cut, a new tip 
is developed. Lateral incisions to produce new roots must go at least half way 
through the plerome. Unless such an incision is made just back of the tip a 
new tip is soon organized immediately above the cut. The original tip is pushed 
to one side and finally is displaced entirely. When the incisions are made on 
two opposite sides of the root at different levels, new root primordia arise at each 
place, but only the one nearest the original tip continues to develop. If two 
incisions are made, on opposite sides and at the same level, a new root arises at 
each, but one is soon suppressed, while the other develops and finally replaces 
the original tip. About forty-eight hours after the wounding, starch usually 
appears in the cells of the periblem just above the cut. The grains are not yet 
3 NEmec, B., Studien tiber die Regeneration. Imp. 8vo. pp. 387. figs. 180. 
Berlin: Gebriider Borntraeger. 1905. M 9.50. 
