Reduction in Descent. 
133 
laid down, there is formed, at the sides of the diarch xylem-plate, a 
certain amount of metaxylem which is sometimes even produced by a 
cambium. This metaxylem often reinforces the primitive protoxylem 
strand of the cotyledon trace, passing off laterally 1 immediately within 
the primary phloems at a later stage of development, and being continuous 
with the metaxylems of the cotyledonary bundles. These metaxylem 
“ wings ” evidently correspond to the xylems of the four bundles repre¬ 
sented in Miss Sargant's Fig. 10, and on the hypothesis of reduction would 
represent the two protoxylems of the root-stele which are supposed to have 
disappeared. But of the supposed primitive division of the first formed 
cotyledon traces themselves there is, in the majority of genera, no 
indication whatever. 
We are asked, in fact, to accept a hypothesis of reduction of the 
primordial hypocotyledonary stele solely on the evidence of a single type 
with a tuberous hypocotyd, a structure quite exceptional in the family, as 
against what seems the plain interpretation of the perfectly normal 
h} r pocotyls of the other genera. No special cause is adduced to account 
for such a reduction. Surely the more natural alternative is to suppose 
that the peculiar vascular structure of Eranthis is a direct outcome of its 
peculiar hypocotyl, the wings of the diarch stele being isolated in their 
upward course through the swollen hypocotyl, while the two original 
protoxylem strands split into four, to join again at the top of the tuber. 
We can hardly consider an arrangement found only in connexion with 
an admittedly modified structure as primitive, and explain the arrange¬ 
ment found in the rest of the family as “ reduced,” without very strong 
independent evidence for such hypothetical reduction. 
I am, Sir, 
Yours, etc., 
University College, June, 1902. A. G. Tansluy. 
1 Spiral tracheitis are often formed at the inner limit of these metaxylem strands in the 
upper part of their course, but this phenomenon seems to be simply in connexion with the 
continued elongation of the hypocotyl after these strands have begun to develop. 
A REVISION OF THE CLASSIFICATION OF 
THE GREEN ALG/E 
BY 
F. F. Blackman, 
University Lec-turcr in Botany, (Cambridge. 
AND 
A. G. Tansley, 
Assistant Professor of Botany , University College, London, 
(continued from page 120 .) 
6. Stvuvca. Sonder, 1845. 
Thallus consisting of an erect stout unseptate stalk, 
terminated by a symmetrical frond of definite form 
which is made up of a very regular system of 
septate filamentous branches fastened together to form 
an open network by rhizoid-like attachments 
(“ tenacula ”) at the points of contact. 
