98 Williamson. — Some Experiments on the Action of 
The Scotch Pines that gave reverse images were examined with special 
reference to the distribution of resin ducts, since it was thought that some 
difference in the number of resin ducts in the autumn wood might account 
for the reversal. However, it was found that numerous resin ducts were 
present in the autumn wood of the heated and unheated pieces of all the 
specimens used, whether they gave the ordinary or reverse image. What- 
ever the cause of this reversal of image in some Scotch Pines, there is no 
doubt of its occurrence, and it certainly weakens the case for using this 
method for identification purposes. Images of Larch were obtained in the 
same way. Four specimens were chosen and two pieces taken of each, 
dried at ioo° C. and air-dried. In these cases the spring wood was negative 
and the autumn wood positive in each one. It would be necessary to use 
this method with many more specimens before it could be deduced that 
a reversal never takes place in the Larch. 
The same method was used with examples of timber from other 
Coniferae, with the result that they were found to fall into two categories : 
Spring ivood + and AiUumn wood— 
Pinus sylvestris (usually) 
,, cubensis 
„ palustris 
„ mitis 
„ Khasia 
„ longifolia 
„ Merkusii 
,, Pinaster 
Spring wood — and A utumn wood + 
Larix 
Pseudotsuga Douglasii 
„ Taxifolia 
„ macrocarpa 
Picea 
Abies 
Agathis Australis 
Podocarpus Totara 
Cupressus Lawsoniana 
Pinus Strobus 
excelsa 
Lambertiana 
>5 
Pinus Gerardiana 
These results show that the Coniferae can be divided into two groups 
according to their type of activity on a photographic plate. An examina- 
tion of these two groups shows that the first consists of Pines, which all show 
certain morphological features. That is, they all have diploxylic needles ; 
their leaf-sheaths are not deciduous ; their cone- scales have a central umbo 
each, and the ray-tracheides bear denticulations on their walls. These Pines 
also agree in producing an image on a photographic plate in which the 
spring wood is positive and the autumn wood negative. 
The second group consists of other Conifers and that class of Pines 
that have haploxylic needles, their leaf-sheaths deciduous, their cone-scales 
each with a terminal umbo, and the ray-tracheides bearing no denticulations 
