INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 747 



The pollen-tube is developed from the larger cell. In certain 

 cases the vegetative cell (or cells) takes no part in this process, the 

 nucleus and other contents of the larger cell only passing into the 

 tube. But usually the separating wall is resorbed. It may disappear 

 almost immediately after the division, but in most cases endures for a 

 certain time ; the entire vegetative cell (or cells) separates itself from 

 the inner wall of the pollen-grain, and is thus surrounded by the 

 larger cell, assuming a peculiar spindle or crescent shajie. The 

 vegetative cell may remain for a longer or shorter period in this con- 

 dition ; or its nucleus divides, and fresh cells are thus formed by free 

 cell-formation. In both cases the protoplasmic membrane is finally 

 resorbed, either in the pollen-grain itself, or after the vegetative cell 

 has passed into the pollen-tube. After the disappearance of this 

 membrane, a further division of the naked nucleus may take place, 

 either in the grain or in the tube. The nuclei often have a peculiar 

 form. 



Except in the case of the Cyperacete, no division of the nucleus of 

 the larger cell was observed. 



No definite order is usually maintained in the passage of the con- 

 tents of the pollen-grain into the pollen-tube. The nuclei are ab- 

 sorbed sooner or later, but always before fertilization. Tlie larger 

 cell and its nucleus api>ear to be of greater importance in impregna- 

 tion than the others. This may be inferred from the facts that it is 

 the larger cell that develops into the tube, and that there are circum- 

 stances in which the nucleus of the larger cell always takes prece- 

 dence in the movement, while the opposite case was never observed ; 

 and even in those plants in which this precedence is not constant, it is 

 still most usual ; as also from certain cases where the vegetative cells 

 remain in their original position within the pollen-grain, and do not 

 enter the pollen-tube. 



The observations were made mostly on monocotyledonous plants 

 belonging to the orders Orchideae, Liliaceae, Irideee, Cyperaceae, &c. ; 

 but some also on dicotyledonous plants, as Latlajrus sylvestris, 

 Plantago media, Eyjyericum cahjcinum, &c. The preparations were 

 made almost entirely with a one per cent, solution of osmic acid. 

 The author found it, however, almost indispensable to use some pig- 

 ment after fixing the preparation with osmic acid ; and for this 

 purpose he found the best to be a solution of carmine to which some 

 glycerine was added. By this means, after about twenty-four hours, 

 preparations were obtained which left scarcely anything to be desired 

 as to clearness. 



In order to see the growth of the pollen-tube, recourse must bo 

 had to artificial culture ; and for this purpose many sorts of solutions 

 were used, and of very different degrees of condensation ; but in the 

 end the author came back to a simple solution of sugar. In some 

 cases weak solutions were rec[uired, and in others strong ones. The 

 culture was generally made in the dark, and at a summer temperature, 

 but some grown in daylight succeeded admirably. 



On three plates the difterent forms to be met with in some twenty- 

 three species of plants are represented. 



