76 SPERMATOGENESIS AND FECUNDATION OF ZAMIA. 
dorum, Guignard (49) describes the occurrence of definite granules at 
the poles of the spindle which seem to be similar to centrosomes. He 
claims that the occurrence of multipolar spindles can not be taken as 
evidence of the nonoccurrence of centrosomes, as the multipolar spindle 
in which a definite granule may occur at each pole evidently later 
becomes bipolar by the various polar ends of the spindle swinging 
around together and uniting in such a manner as to form a normal 
bipolar spindle. Schaffner also claims to have found bodies which he 
calls centrosomes at the pole of the spindle in Sag7ttarca (99), and in 
root tips of Addiwm cepa (100). Fullmer also claims to have found cen- 
trosomes in the seedlings of Pinus larico and P. sylvestris (41). Even 
considering the claims of Guignard, Schaffner, and Fullmer for the 
presence of a centrosome in certain Spermatophytes, their occurrence 
is still a question of grave doubt. The very careful and complete 
researches of Osterhout (94), Mottier (87, 88, etc.), and many others, 
where no indication of a centrosome has been found, throw a doubt 
on the matter, and their presence must be confirmed by other investi- 
gators in those plants where they are said to occur before their normal 
and regular occurrence can be credited. They must be of such a 
nature that they can be demonstrated to occur in the same species of 
plant in the same stage of development by various investigators. If 
we are to recognize evanescent bodies as the homologues of centro- 
somes, our whole idea of the importance and nature of these organs 
must change. 
Our conception of the centrosphere and centrosome is continually 
changing. The original idea of Boveri (17) that the centrosome is ‘‘a 
distinct, permanent cell organ, which, increases by division and sup- 
ples the dynamic centers for the succeeding cell formations,”* has 
been greatly modified by the extensive researches of recent years. 
It is no longer looked upon as a necessary cell organ reproducing itself 
by division, a number of instances being known where they are formed 
de povo in the cell. V arious forms are also known, so numerous that 
there seems to be almost no correspondence between them; still there 
are certain morphological characteristics and certain functions which 
may be said to be common to all centrosomes. The centrosome or 
centrosphere, in its typical sense, as the writer understands it, is an 
organ of the cell, with the following attributes: (1) It is located in the 
center of an aster, at the pole of the spindle during division; (2) it has, 
as its special function—the formation of the spindle and the control 
of the division; (8) it occurs usually, at least, in the division of sexual 
and embryonic cells. | 
In regard to the first of these propositions the writer is not aware 
1“¢ Bin der entstehenden Zelle in der Einzahl zukommendes distinktes dauerndes 
Zellenorgan, das, durch zweitheilung sich vermehrend, die dynamischen Centren 
fiir die Entstehung der niichst zu bildenden Zellen liefert’’ (17, p. 60). 
