﻿1903] NUCLEAR MEMBRANE 307 



archesporial cells of Equisetum limosnm were especially studied, 

 and were selected as types to illustrate the process of nuclear 

 membrane-formation, the results obtained from these forms were 

 confirmed by observations made on several other forms, such as 

 Lilium, Cobaea, Gladiolus, Hedera, Pinus, Pteris, etc, 



Flemming's strong solution of chromic-osmic-acetic acid, 

 diluted with one volume of water, was used for fixing, and the 

 triple stain, safranin, gentian-violet, and orange G, for staining. 

 After being fixed the material was washed in running water and 

 was then dehydrated by being passed through various grades of 

 alcohol. Bergamot oil preceded the infiltration of paraffin. 

 Microtome sections from i to 3.6/^ thick were used. 



THE FORMATION OF VACUOLES AND THEIR RESEMBLANCE TO 



NUCLEL 



To any one who has made a special study of the nucleus, 

 especially of the spore mother cells of the higher plants, the 

 resemblance of this body to a vacuole has probably suggested 

 itself. As is well known, the presence of a vacuole is one of 

 the most striking characteristics of the plant cell. This is par- 

 ticularly so of the mature cells in any vegetative tissue, where 

 the vacuole is quite as constant as the nucleus. The vacuole is 

 not apparent in the very young cell, as the nucleus and cyto- 

 plasm seem to occupy the entire cell cavity. At an early stage 

 in the growth of the cell, however, small lacunae containing a 

 watery fluid may be observed in the cytoplasm. As the cell 

 continues to grow these lacunae become much larger and finally 

 flow together, forming one or more large vacuoles in the cell. 

 As these vacuoles enlarge the cell continues its growth. The 

 amount of cytoplasm, however, does not increase at the same 

 i^ate as the contents of the vacuole. The result is that in the 

 mature cell the vacuole may occupy the greater part of the cell 

 cavity. The watery fluid of the vacuole holds many substances 

 in solution. It may function as a storehouse for reserve food 

 material. It may even contain solid bodies such as starch grains, 

 aleurone grains, and crystals of calcium carbonate or oxalate. 

 Finally the vacuole is always surrounded by a distinct limiting 

 plasmatic membrane. 



