557 
Trow. — On Fertilization in the Sap rolegnieae. 
observed a well-developed nucleus, its centrosome and astrosphere, in close 
association with a recognizable nucleus bearing at one end a few astral rays. 
Some botanists might be prepared to argue from this isolated occurrence 
that a fusion of nuclei takes place at the commencement of ‘ balling.’ 
The more reasonable explanation is, I think, that this solitary super- 
numerary nucleus was the last recognizable survivor of the superfluous 
nuclei, and destined to disappear by degeneration in due course, like its 
fellows. In fact, it would probably have been overlooked had it not had 
associated with it a few astral rays. In the same section two small 
indefinite astrospheres with the nuclei no longer definitely demonstrable 
were noted, viz. at e and f. As ‘ balling 5 proceeds the astrosphere con- 
tinues to increase in size until it is a very conspicuous structure indeed. It 
reaches its maximum development just before the separation of the ‘ origins 5 
in the process of the formation of the oospheres (Figs. 20 and 21). The 
rays of the astrosphere, it will be noted, are mainly directed towards the 
oogonial walls in radial sections. The nucleus has a well-defined nuclear 
membrane, and the chromatin is aggregated at the end nex the centro- 
some, forming there, as it were, a deposit on the inside of the nuclear 
membrane. The nucleus thus acquires at this stage a distinct vesicular 
character — one specially remarkable from the absence of the usual central 
body. At this stage the ‘ origins' are invariably uninucleate. The absolute 
determination of this point is necessary in order to prove fertilization by 
means of the order of succession in the number of nuclei in the oospheres and 
oospores. Eleven oogonia were examined critically. These contained respec- 
tively 5, 13,11, 10, 8,8,9,11, 4, 6, and 14 ‘origins. 5 Ninety-nine origins were 
thus examined. All were uninucleate. Many other oogonia were casually 
examined in the course of the investigation, and in no case were two nuclei 
observed in one ‘ origin. 5 At about this time the fine-grained protoplasm 
surrounding the nuclei in the centre of the ‘origins 5 begins to stain more 
deeply and thus to acquire a certain appearance of individuality. I propose 
to call this central mass of material, for convenience in description among 
other reasons, the ovocentrum. I do not regard this ovocentrum as a 
morphological unit in any sense, but rather as a transitory appearance 
depending primarily upon the forces acting in the oosphere. The materials 
—whether living protoplasm or reserve food products — by virtue of which 
the acting forces put themselves in evidence, play apparently a passive 
part ; to use a hackneyed simile, they behave as iron filings do to a magnet. 
It is to this body that I have hitherto applied in other species of plants the 
term ‘ coenocentrum. 5 It is clear that the term ‘coenocentrum, 5 first proposed 
by Stevens (’ 99 ), and used afterwards by Davis (’ 00 , 5 03 ), Ruhland (’ 03 ), 
myself, and others, has been applied to more than one type of object. 
The use of the term ‘coenocentrum 5 has no doubt facilitated the study of 
the sexual organs of the Phycomycetes, but it can scarcely be regarded as 
Q q 2 
