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380
william rosén
This is quite Ihe same course of development as described above in
Phacelia viscida and divaricata with the difference, however, that Ihe
species last mentioned having not yet reached Ihe nuclear stage of the
endosperm proper.
Another peculiarity is the Lappula-type. There is no doubt that il
is an intermediate type, but its origin is wrapt in obscurity. The fact
that the first wall sometimes is oblique could possibly throw some light
on its origin, that then would be type 3 or i above.
In this family there might be two series of endosperm development,
one having reduced chalazal haustorium and one having reduced
micro-pylar haustorium, both series originating from a Ycrbascum-type and
ending in the nuclear endosperm type.
Three families, Convolvulaceae, Cuscutaceae and Polemoniaceae
(see 17, p. 160, further literature I here) having only nuclear endosperm
are assigned to the Tubiflorae, As to their endosperm we have no
charader suited for deciding anything about their origin. It would be
mere guesswork. By using an analogism a similar origin might be
attributed to them as to Ihe nuclear endosperm in other Tubiflorae
families, or in other words, it may be the most progressive type.
The rest of families classed among Tubiflorae, as far as we know
(see 17, further literature there) have endosperm forms with haustoria
and in all the families the origin of these forms may easily be traced
back lo the VerbascumAype. In Acanthaceae, however, there is, besides
cellular endosperm forms, a peculiar type having haustoria but the very
endosperm being nuclear and Mauritzon (8, p. 39) declares: »Mil
Sicherheit zu sagen welches von diesen beiden Extremen in der Familie
das ursprüngliche ist, erscheint schwierig oder unmöglich». Yet he
follows the current opinion I hut the cellular endosperm has been
developed from the nuclear one and immediately afterwards he stales Ibis
course of development »als den einzig inöglichen und naliirlichcn».
I am, however, inclined to think that (hese forms having haustoria and
at the same time nuclear endosperm proper may be interpreted as
intermediate forms to the completely nuclear form. They, so to speak,
start their nuclear endosperm before Ihe haustoria have disappeared,
they start at an earlier stage than for instance Phacelia Parryi or
Hyoscyamus. If one compares these Acanthaceae-forms with Ihe
endosperm in Nonnea and Lycopsis one will find that there is in reality
but lillie difference between them. By my above intrepretation the two
species last mentioned have no micropylar haustoria but only a
four-cellular chalazal haustorium and the very endosperm is nuclear. The
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