. i. : _ os 45> ie This seamen of the Segue i 
438 BOTANICAL GAZETTE [JUNE 
observed to occur; so it can be stated without exception that 
this action of the nucleoli in being thrown out into the cytoplasm 
and collected again into the daughter nuclei is the normal pro- 
cess for the whole gametophyte generation of L. Philadelphicum. 
Whether this process will be found to occur in the gametophyte 
generation of all angiosperms, or in all plant cells, is yet to be 
determined. There is often a marked peripheral placing of the 
nucleoli in the daughter nuclei which becomes very striking in 
certain cases where the nuclei lie in just the proper position 
(fig. 47). This would in itself be quite suggestive of the way 
in which the nucleoli were formed, even if they were not seen to 
enter from the outside. 
The micronucleoli are constantly present in the cytoplasm 
from the time they leave the nucleus until they enter again. 
Of course it may be urged that the original micronucleoli are 
dissolved in the cytoplasm and new ones formed. If this is the 
case the dissolution of old ones and the formation of new ones 
must go on simultaneously. It is not intended to contend here 
that the nucleolus is a permanent cell organ, for more observation 
is needed for such a generalization. But that the nucleoli pass 
out and enter again to form new ones in the daughter nuclei 
cannot be denied. The strongest argument in favor of regard- 
ing the nucleolus asa definite body or organ seems to the writer 
to be the fact that in many plants and tissues the number is 
constant. Thus in many cases the number in each nucleus 1s 
almost absolutely constant. Are such examples of constancy at 
hand for other excretions or food products? That the number 
is often variable is no argument against its fundamental char- 
acter. The number of nuclei in many cells is also exceedingly 
variable. 
ms During the ents of the nuclei in the embryo sac the 
spindle threads undergo a thickening in the middle as though a 
nuclear plate’: and cell-wall were to be formed (jigs. 38-47), and 
— the spindle o often persists one division to another, so that 
four daughter ole may seaent to be connected by three 
