22 
Tans ley and Chick . — Notes on the 
It is a striking fact that all these species 5 however badly 
differentiated in other respects, have the endodermis well 
marked. 
The transition of the rhizome to the aerial stem takes place 
very slowly, and begins very low down, so that the typical 
anatomical characters of the rhizome are lost long before 
there is any alteration in external features. For this reason 
it is necessary to dig up the plants very carefully and obtain 
a considerable length of rhizome in order to get sections 
showing the typical features. A section of P. juniperinum 
cut three-quarters of an inch below the beginning of the 
strictly subterranean rhizoid -bearing portion will often still 
show transitional phenomena. 
The anatomical features of the transition have in the main 
been correctly described by Bastit (op. cit., pp. 356-360, 
Figs. 47-50), though his curious terminology and apparent 
want of appreciation of the real nature of the tissues involved 
considerably detract from the value of his account. 
The first thing that happens is the lateral extension of the 
hypodermal strands. These eventually meet and become 
continuous with the sclerenchymatous outer cortical zone 
of the aerial stem, as Haberlandt and Bastit have stated. 
This zone is already continuous, occupying the whole of the 
cortex down to the endodermis, before the stele loses its 
typical rhizome character. Meanwhile the hydroids have 
increased in size and number, and the larger ones tend to 
concentrate in the centre of the stele while the stereids 
correspondingly become fewer. At this stage the leptoid 
groups are extremely obvious, one or two of the elements 
often becoming very large, and their walls, which are pale 
straw-colour, standing out very clearly from the dark chestnut- 
brown walls of the surrounding tissue. The endodermis 
begins to lose its characters, and, together with the cells of 
the inner part of the radial strand, forms the foundation 
of the inner cortex of the aerial stem. The sides of the stem 
flatten so that it becomes a three-sided prism. The stereids 
of the stele decrease to very few so that the files of hydroids 
