26 INTRODUCTION. 
small ones, at corresponding stages of mitosis. The presence or ab- 
sence of extra-nuclear nucleoli may not depend so much upon the 
plant, perhaps, as upon the condition or activity of the cell, From 
the spindle stage of the first to the end of the second division there is 
no noticeable regularity in the behavior of these bodies. In different 
cells in the same stage of mitosis they may be present or wholly want- 
ing. Even after the daughter nuclei are provided with membranes, 
and a nucleolus is present in each, extra-nuclear nucleoli are to be fre- 
quently seen in the cytoplasm. The same holds also for the second 
mitosis. A careful investigation of the behavior of the nucleolus in 
both Thallophyta and higher plants has shown that the nucleolus 
appearing in the daughter nucleus is not one of the extra-nuclear 
nucleoli which happened to lie near the chromatin, or in such a posi- 
tion as to be included by the nuclear membrane, but that the nucleolus 
arises anew in each daughter nucleus. The nucleolus appearing in 
the daughter nucleus arises usually near or in contact with the chro- 
matin thread, but it is not implied that the nucleolus represents reserve 
chromatin. 
In the higher plants and in those with typical nuclei the morpho- 
logical evidence furnished by a study of karyokinesis, as well as the 
evidence of experimental physiology, goes to show that the nucleolus 
in such plant cells represents so much food material which can be 
drawn upon by the cell according to its needs, Whenever the activity 
of the cell is more intense, the nucleolar substance tends to become 
diminished, and it matters not whether the activity is directed toward 
constructive work or the production of energy. It is true that in some 
cases the food material furnished by the nucleolus seems to be used in 
a large measure by the chromatin, for example, in Déctyo¢a, but in 
others by other parts of the living substance, as in the growth of the 
spindle or cell plate. In certain species of Spzrogyra (Wisselingh, 
’98), in which, as it has been claimed by several investigators, the 
nucleolus furnishes directly one or more chromosomes, greater diffi- 
culties present themselves. It is not improbable that the nucleolus of 
such plants as Spzrogyra may possess a totally different composition 
from that of the typical nucleolus, and we may, therefore, speak with 
propriety of chromatin nucleold. Wowever the behavior of the 
nucleolus is not well enough known in the plant kingdom to justify 
any attempt to harmonize all the facts now known. Applied to the 
higher plants the above conclusion seems to be very reasonable, since 
the facts there are almost wholly confirmatory, 
