Observations on the Anatom} 
Seedlings. 
IV. Further Studies on the Anatomy of Atypical Seedlings 
of Impatiens Roylei, Walp. 
BY 
H. S. HOLDEN, M.Sc, F.L.S., 
AND 
MARGARET E. DANIELS, B.Sc. 
With ninety-seven Figures in the Text. 
HE present paper is the outcome of an attempt to determine the relation- 
JL ships of abnormal seedlings of two types occurring in Impatiens Roylei , 
the anatomy of which has been described in a previous issue of this 
Journal (18). In the normal seedling each cotyledon possesses a median 
‘ double ’ bundle with independent laterals, and shows tetrarch symmetry 
in both hypocotyl and root. The tetrarch condition is reflected in the 
constant presence of a whorl of four lateral roots at the junction of the 
hypocotyl and tap-root. In the abnormal seedlings one type 1 described 
exhibits the characteristic phenomena associated with syncotyly, cotyledo- 
nary fusion being followed either by a precocious fusion of the laterals on 
the symphysis side with the midrib, or by their partial or complete 
suppression. A triarch symmetry is thus produced and is accompanied by 
other related features, notably the development of three members in the 
root-whorl and the elimination of the leaf on the symphysis side at the first 
epicotyledonary node. The second type 2 apparently possesses a single 
cotyledon only, and gives rise to a diarch condition in the hypocotyl, this 
being reflected both in the root-whorl and tap-root. One of the two poles 
in the hypocotyl is a direct downward continuation of the single median 
‘ double ’ bundle : the other results from the fusion of the lateral strands on 
either flank. Only one axillary cotyledonary bud is present, in contrast to the 
two occurring in the first type. The two types approach each other, as far as 
1 Referred to subsequently in this paper as ‘ Type i \ 
2 Referred to subsequently in this paper as ‘ Type 2 ’. 
[Annals of Botany, Vol. XXXV. No. CXL. October, 1921.] 
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