ar wn ve oe
oy
:
netaer
—*
Fig. 5.
chants Be RA hae ee nnn
Sw
RLS GRERMS EL mE
*
eS
The arrow points to a ring chromatid in Artemisia spinescens.
Fig. 6.
The species, Machaeranthera tortifolia came from the experimentally irradiated
plot in Rock Valley, NTS. This species is characterized by six chromosome
pairs consisting of three large and three slightly smaller pairs (Fig. 6). A
large number of extranuclear bodies occur in telophase I and telophase If
(Fig. 7), although they are not as large or prominent as those of Artemisia
spinescens.
Flower buds collected 14 and 29 April 1976 contained meiotic
cells at the proper stage for analysis.
Chromosomal aberrations detected
included five bivalents and two univalents, acentric fragments, and dicentrics
(Figs. 8, 9, 10, and 11; Table 2).
No multivalents were observed. Of the
The normal condition of six large bivalents in Machaeranthera
torttfolia.
came from an area remote to the radiation source where the radiation level
It has been included with the lower level for analysis, howwas background.
A large part of the aberrant cells from the high dose area came from
ever.
a single plant which contained 64% of the anaphase cells showing a dicentric
and/or a fragment (Fig. 11) showing that the plant was heterozygous for a
paracentric inversion.
2,714 cells analyzed, 1,767 came from nine plants with doses ranging from 2.5
The Mann-Whitney test does not indicate significant differences between these
populations.
ated area where the dose rate was less than 1.0 R/day.
The third species krameria parvifolia which came also from the Rock Valley
to 4,5 R/day,
and 947
cells were
from five plants outside
the
immediate irradi-
One of this latter group
site,
360
has six
large chromosomes
(Fig.
were collected on 19 and 20 May 1976.
361
12).
Flower buds with meiotic ceils