26. ELEMENTS OF PLANT ANATOMY. 
In cormophytes the presence of one nucleus has been traced 
in nearly all the ving cells. These nuclei are nearly spherical 
in form, their outer portion much denser than the surrounding 
cytoplasm, while the inner is only slightly so. They are largely 
albuminoid in nature. - In the cells of the sexual organs in cer- 
tain stages several nuclei are normally present, and in cells of 
purely vegetative organs a number of nuclei are often found 
after an injury. 
In many of the thallophytes until quite: recently there was 
no definite proof of the existence of nuclei. Now it is claimed 
that by a more successful use of clearing and staining agents, 
nuclei have been found in many algae, in some instances singly 
in a cell, in others in numbers. In the mycelium of many 
fungi a plurality of nuclei has also been determined. 
So far as has been ascertained, the chemical nature of the 
nucleus is the same as that of the surrounding cytoplasm. Its 
physiology is not clearly understood. Formerly it was sup- 
posed to be intimately connected with the process of cell- 
division. It is now known that the two processes, cell-division 
and nuclear division, are not dependent upon each other. Some 
scientists claim that the function of the nucleus is to aid in the 
production of proteid substances, others consider it the medium 
of inheritance, or transmission of characteristics to the succeed- 
ing generation. , 
The number of nuclei is increased only by the division of 
those already in the cell. This division is of two kinds, direct, 
or fragmentation, and indirect, or karyokinesis. 
8. Direct Division of Nucleus. 
This method of division is not preceded by any special 
changes in the constitution of the nucleus, nor is it followed by 
cell-division. In the higher forms of plants there is very good 
evidence that it occurs, but only in a limited number of cases ; 
