62 COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
That, in forms in which a pluricellular megasporangium is pres- 
ent, any or all of the megaspores have the ability to develop into 
embryo-sacs proves in a most convincing manner the morpholog- 
ical equality of the megaspores, and the regular division of each 
of the megaspore mother-cells into four megaspores must be 
regarded as a true tetrad division. 
At this point it is of interest to compare this result with those 
reached by Murbeck * who has studied A/chemilla, a representa- 
tive of the Rosaceae. The presence ofa multicellular archesporium 
in this family was first made known by Strasburger. + According 
to Murbeck twelve to sixteen mother cells are present, of which 
the peripheral and usually one of the centrally placed, fail to 
divide, and moreover never give rise to embryo-sacs. The re- 
mainder, six to nine in number, divide at least once and of the 
daughter-cells some divide a second time, and the granddaughter- 
cells thus formed are regarded, properly, as megaspores, It may 
be noted in passing that here there is no reduced number of chro- 
mosomes, reproduction being parthenogenetic. Of the megaspores 
thus produced, two or more may develop into young embryo-sacs, 
and what is of immediate and special interest in this connection, 
in the same Sporogenous cell-row, tivo or more may commence their 
development into embryo-sacs. It thus appears that Alchemilla and 
Crucianella are precisely comparable in this regard; while the evi- 
dence derived from the latter is still more final because of the 
actual division of all the megaspores derived from a simple mother- 
cell. Further cytological evidence that these are to be regarded 
as true tetrad divisions is presented on another page. 
It is scarcely necessary to add that these facts accord an extra- 
ordinary strength to the view that the ovule is a sporangium. 
In the Spermacoceae and Oldenlandeae the archesporium con- 
tains only one megaspore mother-cell of special size, from which 
the embryo-sac cell is derived. Several suppressed megaspores 
are present, surrounding the large megaspore mother-cell, which 
divides to form four megaspores, the basal of which forms the 
embryo-sac cell. 
ee Embryobildung in der Gattung Alchemilla. Acta. Reg. Soc. 
۱ , 11: No. y. I. Fora more extended examination of the relevant 
literature see this valuable paper. 
Angi 
f Die ospermen und Gymnospermen, 
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