264 Pr anker d. — On the Structure and Biology of 
primitive, but Miss Thomas kindly informs me that she has since often 
found it, and that it occurs in other members of the Primulales. Of the 
' double bundle ’ ( 14 ) so widespread in its occurrence, I find no trace in 
Hottonia. 
A little plantlet which has produced about fourteen leaves and an 
adventitious root is drawn in Fig. 16, PL XXL Fig. 21 shows a transverse 
section of the stem, the stele of which consists of two xylem elements placed 
centrally, surrounded by small, delicate cells, presumably phloem, and this 
by a ring of large cells with well-marked endodermal thickening. The 
cortex is already developing lacunae. 
IV. Theoretical Considerations. 
From the anatomical standpoint, interest centres in the great divergence 
of structure shown in different parts of the plant, and especially in the 
polystelic phase exhibited in the region transitional from the aquatic to 
the aerial type. It may first be noted that the repeated statement to the 
effect that Hottonia has no true pith, but a central mass of wood paren- 
chyma, in which may be found the remains of the first-formed tracheides 
(Solereder (11), p. 504), is incorrect. The ground of this statement is 
doubtless the thickened ring or core of cells in the pith described above. 
Had these structures been always as clearly defined as those shown in 
Figs. 9 and 10, instead of exhibiting great irregularity in transverse sections 
taken at different levels, they would probably never have been confused 
with protoxylem elements ; though any transverse section shows that they 
are always placed more or less centrally, unless the section is taken quite 
close to the whorl of branches, and even here they are separated from the 
wood by several layers of parenchyma. Longitudinal sections, however, 
show conclusively that the cells are irregularly thickened, with no trace of 
spiral or annular markings, and clearly distinct from the protoxylem, which 
is quite characteristic, though often slightly disorganized by the stretching 
of the internodes. However ‘ true pith ’ may ultimately be defined, there 
seems no reason why the claim of Hottoriia to its possession should be dis- 
allowed. 
But if the thickened cells of the pith are not protoxylem, neither are 
they merely the lignified pith of frequent occurrence in Dicotyledons, for 
they have been shown to be in direct connexion with the internal thickened 
ring found at the base of the inflorescence, which when young is a character- 
istic endodermis. Physiologically, the appearance of this tissue may be 
due to the great strain placed upon the stem at the insertion of the whorl 
of branches, and the importance of strengthening their connexion with the 
main stele to prevent detachment. It is true that H. inflata does not 
possess an internal endodermis, but here both the structure and mode of 
