46 INTRODUCTION. 
At the present writing it is the opinion of the author that individu- 
alized centrosomes or centrospheres do not occur in plants above the 
liverworts, and they are certainly absent in certain species of these 
(Axthoceros). On the whole, these structures are well established in 
only a few Thallophyta. 
As the writer has already stated in a former paper (Mottier, 1900), 
if we take into consideration only such plants as Fucus, Stypocaulon, 
Dictyota, and certain Ascomycetes, there are good grounds for the 
view that the centrosome is an organ of morphological value; but the 
evidence furnished by these forms, however convincing it may seem, 
is not quite sufficient, especially in the light of our knowledge of kary- 
okinesis in forms in which centrosomes or centrospheres have not been 
found; for there is no reason for believing that the spindle fibers in 
plants devoid of centrosomes are of a different substance from the 
radiations or spindle fibers developed in connection with an aster. 
Space will not permit of a discussion of such questions as whether 
the radiations are outgrowths of the centrosome considered as a mor- 
phological unit, or constructed out of the kinoplasm by the centrosome, 
or whether the centrosome is only a denser mass of kinoplasm, formed 
by the meeting of the polar radiations, and which may persist after the 
radiations and spindle fibers have disappeared. It may be stated in 
this connection that in plants there is little to support the view that the 
radiations are centripetal or centrifugal currents. They do not seem 
to be currents at all. We understand radiations and spindle fibers to 
be fine, more or less homogeneous, kinoplasmic threads which are 
capable of contracting, extending, or becoming changed into a uniform 
and homogeneous mass. 
We have now to consider the relation of the centrosome to the 
blepharoplast, or cilia-bearer, which is so well known in the sperma- 
tozoid of the Archegoniates (see Chapter V). 
Belajeff, Ikeno, and Hirase and a few others regard the blepharo- 
plast of the fern and certain gymnosperms as the homolog of the centro- 
some. It seems to the author that such a conclusion is merely a hasty 
judgment, which does violence to the facts as they are known at present. 
The development and function of the blepharoplast, as will be seen 
from the chapter referred to, shows clearly that this structure lacks the 
more essential distinguishing characteristics of the normal centrosphere, 
as it is known in the cases most thoroughly investigated. The bleph- 
aroplast is not the center of kinoplasmic radiations which form a 
karyokinetic spindle. So far as has been shown the radiations of the 
blepharoplast primordia take no part in the formation of the spindle. 
These primordia do not divide to give rise to new blepharoplasts, but 
