718 THE AMERICAN NATURALIST.  [Vor. XXXIX. 
tophytes). They sometimes approach the centrosphere very 
closely in their morphology. 
The third and highest type of spindle formation in plants is 
that illustrated in the mitoses within the spore mother-cell which 
were given special treatment in Section III (Amer. Nat., vol. 38, 
p. 725, October, 1904). In this remarkable cell the spindles 
develop from a mesh of independent fibrilla which at prophase 
more or less completely surround the nucleus. The poles of 
the spindle arise by the grouping of cones of fibrillz so that a 
single axis is finally established but without any kinoplasmic cen- 
ters at the poles. This type of spindle formation which may be 
termed the free fibrillar type is one of the most interesting 
cytological peculiarities of plants. It has been found in all 
types whose sporophytic phase terminates its history with a 
spore mother-cell, although the accounts in the Hepatice are 
not in full accord. 
Is it possible to connect the various types of spindle formation 
with one another and to establish any evolutionary tendencies in 
the processes involved ; and have the different manifestations of 
kinoplasm such as centrosomes, centrospheres, polar caps, free 
fibrillar condition, and the mysterious structure called the ble- 
pharoplast any genetic relation to one another? The confusion 
is so great among the thallophytes that the author sees little 
hope at present of establishing clearly any relationships between 
the types of centrospheres and centrosomes with their systems 
_ of radiations (asters) and we must patiently wait for more infor- 
mation. And respecting the origin of these structures from the 
simpler types of mitosis we are absolutely in the dark. But 
the relation which polar caps and the free fibrillar type of spin- 
dle formation bear to centrospheres is less perplexing and it 
seems possible to define certain common features among these 
structures which hold them together with a degree of unity in 
their relations to mitosis. That phase of the subject will be 
considered in this treatment. The Hepaticz as a group occupy 
an interesting position with respect to the character of mitotic 
phenomena at various periods of ontogeny, between conditions 
in the pteridophytes, which are obviously similar to the sperma- 
tophytes, and conditions in the thallophytes. This was brought 
