150 Barber . — The Structure of P achy theca. II. 
firmed by the study of certain other parts of the section, and, 
more emphatically, by other sections still to be described. 
Finally, although these tubes are exceedingly regular and 
quite distinct at the centre of the section, they anastomose in 
all directions at a short distance from it — a fact irreconcilable 
with the view that theirs is a typical cell structure. 
Section 4 is a tangential one, and presents a number 
of yellow tubes cut across transversely at the centre of 
the preparation, more or less obliquely peripherally. The 
yellow tubes are separated by open spaces, or, more usually, 
by an opaque, dark brown matrix. 
While these tubes are circular at the centre of the section, 
a considerable amount of anastomosis occurs at a short dis- 
tance from it — an arrangement discountenancing the idea 
that they are the sections of cells. Each tube has a well- 
marked darker thick concretionary wall similar to those 
already described for Fig. 2 a. The interior of each tube has 
a bright yellow matrix with few granules ; and frequently the 
centre of the tube is occupied by a smaller one, or a sharply 
defined double circle, exactly resembling the surface view of 
a bordered pit of Pinus. A fusion of the smaller tubes is 
never seen, but, where anastomosis of the larger tubes occurs, 
the smaller ones are found in different parts of the yellow 
matrix at about their normal distance apart. 
In this case the smaller tubes are the remains of the cells 
of the plant, the yellow matrix of the larger tubes being the 
mineral collected around and infiltrating these. Where the 
larger tubes are in contact, a fusion of the mineral has taken 
place, and the result is an apparent anastomosis. 
A close comparison between specimens 2 and 4 suggests 
that the great difference in appearance is due to the relative 
quantity in the two cases of the yellow matrix in which the 
smaller tubes are always imbedded. While in section 2 there 
is a preponderance of this substance in the section, in section 
4 there is a preponderance of the dark brown mass. In both 
cases these two constituents of the section are separated from 
one another by the well-marked limiting layer. 
