196 
Hill and de Fraine . — On the 
complex, are not nearly so complicated as in Mirabilis , nor do the bundles 
form two distinct zones. 
M. divaricata :, Lowe, in essential features is like M. longiflora , only two 
points of difference having been observed : in M. divaricata the bundles 
corresponding to c. 17 and c. 18 in Diagram 7 are never collateral, and the 
tetrarch root-structure becomes reduced to diarch. 
M. multiflora , A. Gray. Out of a large sowing there was obtained but 
one seedling, which was of interest owing to the small size of one cotyledon 
(Fig/8) and to the presence of a prominent peg. Unfortunately an accident 
happened to the series of microtomed sections, so that we have no observa- 
tions to make regarding the structure of the upper part of 
the hypocotyl ; sufficient preparations remained, however, 
to indicate pretty strongly that the fundamental features 
of the transition are essentially the same as in other 
species of Mirabilis. As has already been remarked, the 
tetrarch root-structure becomes reduced to diarch. 
This also is true of M. Jalapa , for Van Tieghem 1 found 
that out of ten seedlings examined six had diarch roots and 
four tetrarch. 
From Gerard’s 2 account it is clear that the transition 
phenomena of M. Jalapa are of the same nature as those 
of the species described above, particularly M. divaricata , 
for M. Jalapa shows the same reduction of tetrarchy to 
diarchy. 
With regard to the behaviour of the traces within the. 
hypocotyl we are not in agreement. Gerard observed the 
double series of bundles (Diagram 7, Fig. 5), but he con- 
Fig. 8. Mirabilis sidered that those of the cotyledonary series, not the 
Naturafsize. plumular, moved outwards to form the outer zone (see 
Diagram 7, Figs. 2 and 3). Apparently also Gerard did 
not make any observations on the behaviour of the bundles within the 
cotyledons, and therefore did not realize that the transition really begins — 
or ends, according to the direction the tracing is done — in the seed-leaves ; 
consequently we do not agree that the protoxylems of the root play no 
part in the orientation of the bundles. 
Summary and Conclusion. 
1. The transition phenomena of all the seedlings examined of the 
Natural Orders Portulacaceae, Caryophyllaceae, Amarantaceae, Chenopo- 
diaceae, Phytolaccaceae, and Aizoaceae follow Van Tieghem s type 3 ; 
whilst those of the Nyctaginaceae follow a course which at first sight appears 
distinctive, but is clearly a modification of this same type. 
1 loc. cit. 2 loc. cit. 
