Tasre III. Anaphase I bridges formed during microsporogenesis 
in D. candida cultivars. 
Total No. PMC’'s % PMC’'s observed % 
PMC’s with A I with A I abnormal 
Cultivar observed bridges bridges pollen 
*Buyés’ 213 35 16.4 ‘e.A* 
‘Ocre’ 358 64+ 17.9 50.8 
*Amaron’ 1000 30 3.0 32.8 
‘Culebra’ 537 97 16.9 83.3 
**Buyés’ trees eand fonly. 
bridges in ‘Culebra’. The chromosomal irregularities 
leading to the formation of anaphase bridges are un- 
known. In many cases the bridges were accompanied 
by one or more fragments, implying that chromosomal 
inversions are responsible for some, but not all of the 
observed bridges. 
Pollen abortion 
Preliminary examination of the pollen of D. candida 
‘Culebra’ disclosed a predominance of small, either 
spherical or misshapen, spores among the large and well 
sculptured ones. I decided to investigate for compara- 
tive purposes the frequencies of such abnormal pollen in 
all of the D. candida cultivars. In all but two cases, a 
minimum of two widely separated trees was examined, 
one by myself and one by an assistant. The results of 
these examinations are recorded in Table IV. 
It can be seen that the production of abnormal pollen 
ranges from a low of 5.7 percent in ‘Dientes’ to a high 
of 83.8 per cent in ‘Culebra’. As had been thought from 
purely morphological evidence, the cultivars ‘Buyés’ and 
‘Dientes’ do not consist of a single clone each; with both 
groups there are widely differing capacities to produce 
normal pollen. 
Some of the abnormal pollen may be accounted for by 
the inequality of meiotic products resulting from ana- 
[ 173 | 
