hot 
1898-99.] |. MORPHOLOGY OF THE CENTRAL CYLINDER IN THE ANGIOSPERMS. 613 
which as is usual, cause no gaps in the fibro-vascular tissues, by their 
exit from the stelar tube. 
The foliar vascular strands in both these species are generally 
throughout their cauline course collateral in structure, but early in their 
petiolar course, they become concentric. In these features, they 
resemble the leaf-traces of Primula japonica and P. denteculata described 
by Gwynne-Vaughan.” 
It is undesirable, for reasons already mentioned, to describe further 
the anatomy of the Saxifragacez at the present time, and the subject of 
Polystely may be left with a brief summary of the writer's conclusions. 
From the study of the development of the so-called polystelic central 
cylinder in the vascular Cryptogams and in the Angiosperms, the 
writer has reached the following conclusions: (1) Polystely (so-called) 
does not arise by the repeated bifurcation of the primitive epicotyledonary 
central cylinder. (2) The young central cylinder of this type is primitively 
tubular and is characterized by the occurrence of gaps in the wall of the 
stelar tube corresponding to the leaf-traces. These essential features 
may subsequently be obscured by the passage of numerous traces to the 
same leaf, by the overlapping of the foliar gaps of different nodes, and 
by the development of an internal or external system of strands (or 
both) derived from the original stelar tube. (3) If the above conclu- 
sions be accepted, the terms Polystely and Gamostely should apparently 
be abandoned, since they involve an erroneous conception of the mode 
of development of the central cylinder in the various forms described 
above. The writer proposes as more accurately describing the 
nature of the central cylinder in this type, the term siphonostelic.” 
THE; ASTELIC TYPE 
In his essay on Polystely, already often quoted, Van Tieghem 
describes a modification in the central cylinder of vascular plants, which 
he calls astelic. In this type, the epicotyledonary stele, having 
previously become expanded and medullated, is said to become further 
changed by the sinking in of the endodermis between the bundles. In 
this case, according to Van Tieghem, the endodermis is apt to break at 
the bottom of the undulations between the bundles, and the thus 
separated segments then envelope the several vascular strands with 
31. Op. Cit., p. 312. 
32. Originally suggested in Trans. Brit. Ass. Adv. Sci., 1897, p. 869. 
