1902} MICROSCOPICAL JOURNAL. 63 
companiments, The author then showed the great vari- 
ations in the sizes and shapes of the parts of thevalves 
which were cast by different species, and stated his belief 
that such variations were of value in determining species. 
The real uses of the marginal thickenings of the valves 
and the membrane surrounding the egg were suggested. 
A paper, by Mr. E. M. Nelson, F. R. M. S., “On the Black 
and White Dot,’ was read by the Secretary. The author 
asked indulgence for what might appear a puerile subject, 
but claimed that a proper understanding of the forma- 
tion of the diatomic images must be the prelude to the ac- 
ceptance of any theory of microscopic vision. He then 
proceeded to criticise the papers read earlier in the year 
by Mr. Rheinberg and Mr. Stokes, rejecting the “special” 
theory of the formation of the ‘black dots” made out by 
the former, and, though agreeing with much that the lat- 
ter had stated, putting forward evidence which he believed 
to be in opposition to some of Mr. Stokes’s conclusions. 
ABNORMAL SECONDARY THICKENING IN CLIMBING PLANTS. 
—In its summary ot botany at the last meeting of the Brit- 
ish Association, ‘‘Nature” mentions a paper by Miss A. 
M. Clark in which the author describes the process of for- 
mation of the abnormal secondary thickening in Ken- 
drickia walkeri, a tropical epiphytic climbing shrub. The 
anatomy of the young stem is typical of the family Mel- 
astomaceae. At an early stage numerous small patches 
and several large wedge-shaped areas of thin-walled un- 
lignified wood-parenchyma are cut off from the inner side 
of the completely circular cambium ring. Tylosis is of 
frequent occurrence, and the tylosed cells may develop 
into sclerotic cells inside the vessels and tracheids. At 
a later stage the unlignified wood-parenchyma cells, at the 
central margin of the wedge area, take upon themselves 
new growth accompanied by cell-division. The product of 
this new growth proceeds to split the axial woody ring ° 
