32 THE CELL 



even put forth delicate processes, whereas on the other side its contour 

 remains sharply denned. From the position taken up by the nucleus, 

 and from the Local increase of surface which it exhibits, Magnus quite 

 properly concludes that this organ enters into active communication 

 with the protoplasmic sheath, while the latter is undergoing trans- 

 formation into cellulose. A very similar state of tilings has been 

 observed by Shibata in the rhizome of Psilotum triquetrum. Here, 

 again, the nuclei of the digestive cells are provided with amoeboid 

 processes, and are situated close to the hyphal clumps, or actually 

 adhere to the latter. In Psilotum a substance akin to amyloid is 

 produced in place of cellulose for the purpose of cementing the clump 

 together. In the galls produced on plants of Zea Mays by Ustilago 

 Maydis, the hyphae of the parasite, on penetrating into the cells 

 of the host, often become enclosed in a fairly thick sheath of cellulose 

 secreted by the protoplasm of the host. Guttenberg describes the 

 behaviour of an infected cell as follows : The nucleus moves towards 

 the invading hypha, which thereupon rapidly becomes enveloped in 

 cellulose ; if the hypha continues to grow, the nucleus, which 

 frequently assumes a lobed form, remains near the advancing apex, 

 while the cellulose sheath is gradually extended. 



If the nucleus really is the vehicle of the idioplasm, its controlling 

 influence obviously cannot be confined to those ontogenetic processes 

 which are concerned with the secretion and growth of the cell-wall. 

 On the contrary, the nucleus must exercise some control over all 

 the various components of the developing cell. But the nature of the 

 subject is such, that very few data are as yet available, apart from 

 the above-mentioned observations with regard to the formation of 

 cellulose membranes. Tor the present, therefore, it must suffice to 

 remark, that there are a number of circumstances which indicate that 

 the nucleus exerts a certain amount of influence upon the growth and 

 division of chromatophores. In the young cells of Higher Plants, 

 the chromatophores either take the shape of pale-green chloroplasts, 

 or else are present in the embryonic form of leucoplasts ; in either 

 case they are, to begin with, usually aggregated around the nucleus, 

 and for a time grow and divide in this position. In species of 

 Selaginella the author finds, in each cell of the fundamental meristem 

 of I lie stem-apex, a single pale-green chloroplast, which almost 

 invariably lies in close contact with the slightly larger nucleus. By 

 repeated division this original chloroplast gives rise to a chain of 

 chlorophyll-corpuscles, which at one point still remains in close 

 relation with the nucleus. It occasionally happens that the original 

 chloroplast is at first not actually in contact with the nucleus, but is 

 only indirectly connected with it by means of a protoplasmic strand; 



