FORM OF THE PLANT- CELL. 33 



sentschaftliche Botanik.) He has proved the existence of the cytoblast 

 in all the families of the Cryptogamia, especially the Algce, and shown 

 that it is necessary to distinguish between a parietal and central nu- 

 cleus.* The central nucleus subsequently becomes hollow, and may 

 be increased by division. I cannot, however, agree with Nageli when 

 he asserts that the cytoblast consists of an external membrane, with con- 

 tents. I regard this as a later stage of their development, for in the 

 young free cytoblasts there is no trace of a distinct membrane, and the 

 origin of the free cytoblast forbids such a supposition. Observation, 

 however, on this subject is not yet brought to a close ; and many things 

 will occur to modify, extend and explain our present knowledge. 



Complete Observations upon the Formation of Cells. I. When the 

 cytoblasts are perfectly formed, they soon present a delicate membrane, 

 which encloses them, and which is sometimes extremely fine and soft, 

 and sometimes thicker and more compact, t This membrane soon 

 becomes elevated on one surface of the cytoblast in a vesicular form, and 

 gradually extends itself, so that the cytoblast occupies at last only a 

 small part of the wall J ; but still the cytoblast continues to enlarge, and 

 the nucleoli become more evidently defined. The membrane of the 

 vesicle, or young cell, becomes gradually stronger and thicker ; it gets a 

 round, or sometimes an elongated, form, and sometimes an irregular edge, 

 which subsequently disappears. 



In the youngest state of the cell the cytoblast is generally covered on 

 all sides by a delicate membrane, which is not coloured by iodine. Mohl 

 (Botan. Zeitung, 1844) has clearly not understood my observations in 

 the paper which I published in Miiller's Archiv for 1838, and in which 

 I first made known my discoveries on this subject. As soon as this 

 primary cell membrane is removed by extension, at some distance from 

 the cyloblast, it is often found covered with a delicate layer of semifluid 

 mucus, which is sometimes seen circulating in little anastomosing streams, 

 sometimes granular, sometimes entirely homogeneous and clear, and which 

 when present may be made visible by the action of nitric acid, alcohol, and 

 iodine. This is Mohl's primordial utricle. It is directly on the bound- 

 ary between the membrane and its contents, that the most active chemical 

 processes take place ; and this goes on as long as the necessary conditions 

 are present, especially the formation of nitrogenous matters. It is, 

 therefore, not improbable that this layer is the agent in converting the 

 newly introduced constituents of the cell into cellulose, and thus of thick- 

 ening its walls (or even forming new cells). But at last these protein- 

 layers are dissolved and decomposed, and disappear. In old cells, 

 especially of wood, no trace of these layers is found, and generally only a 

 small quantity of nitrogenous matter at all. I can understand how it is 

 that Mohl may doubt the existence of a membrane free from nitrogen, for 

 I am far from asserting that my observations are complete ; but I am at 

 a loss to explain how Unger can affirm that the cytoblast is first formed 

 after the development of the cell-membrane. (Linnaea, vol. xv. part ii. 

 1841.) I have just been examining (June, 1845) the spongioles of 

 Cypripedium Calceolus and Neottia Nidus avis ; and although at first 

 I was doubtful as to whether any thing existed besides the great cyto- 

 blast, yet, when I employed nitric acid and iodine, I found surrounding 

 the cytoblasts cells which required a longer period for development in 



* See Nageli on the Formation of Cells, translated by A. Henfrey for the Ray So- 

 ciety. 1845. TRANS. 



f See Plate I. figs. 1. c, 4. c. \ See Plate I. figs. 1 . d, 2. 14, 15, 1G. 



D 



