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306
is less precision in the different stages than in the heterotype. The
partners of the bivalents are segmented and their halves pass to
the poles. The same behaviour is shown, in many cases, by the
descendants of the singles too. In the telophase a new elimination
of the last mentioned chromosome elements takes place, the four
ordinary microspores (containing the descendants of the gemini
Fig. 2. a. R. (Coriifoliae) *solanifolia Matss. Diakinesis showing 7 bivalent and
21 unpaired chromosomes. b. R. glutinosa Sibth. & Sm. *libanotica Boiss, Meta’
phase showing 7 bivalents and 28 singles in the same plane. c. R. (Tomentosae)
*subcristata Schz. Interkinesis after the heterotypic division showing two great and
some small nuclei.
Same magnification as in the first plate.
thus obtaining only a few or sometimes none of them. In that
way, the chromosome number of these pollen grains will be rather
small, sometimes only 7. All the other microspores — there arises
a great number of them from each pollen mother cell — contain
only descendants from the univalent chromosomes, and their chro-
mosome number then often will be still smaller.
13. Some of the microspores, probably those containing the
descendants of the bivalents, develop into pollen grains and can
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