374 XXVII. REPRODUCTION OF GYMNOSPERMS. 



gonium is an oosphere (o), which in alcohol material is noticeable 

 from its yellow-brown colour, and shows a central large nucleus 

 (in) ; and lastly, under the ovule, the commencement of the wing 

 (s). If we prepare a similarly-directed section through a fresh 

 ovule of the same age, we shall again find the same relations ; but 

 very commonly the contents of the archegonium will have run 

 Out. If the section has laid bare individual archegonia, without 

 opening them, the oospheres will appear as yellowish frothy 

 masses of protoplasm, in which the central nucleus is scarcely 

 distinguishable, or else, in the best cases, has only the appearance 

 of a large central vacuole. The oospheres quickly suffer under 

 the influence of the water taken from their environment ; if the 

 section is to be kept for a longer time, it is recommended to use 

 as fluid for observation white of egg diluted with water, to which, 

 for greater stability, a little camphor has been added. In such 

 preparations the neck of the archegonium is not difficult to see. 

 It consists of from two to four stages of cells. Under the neck is 

 to be found a small cell (Fig. 137, A, cl), which corresponds with 

 the ventral canal -cell of the Vascular Cryptogams ; the oosphere 

 divides, in order to form it, shortly before it is receptive. The 

 venter, or body, of the archegonium is surrounded by a layer 

 of flattened cells, rich in cell-contents. In order to inform our- 

 selves as to the number and position of the archegonia, we prepare 

 a number of successive cross-sections through the upper part of 

 the ovule. In this way we show that from three to five arche- 

 gonia, arranged in a circle, stand at the apex of the embryo-sac. 

 Sections which have laid bare this apex show us the neck of the 

 archegonia, in apical view, as rosettes of six or eight cells. 



Fertilisation. If our material has been gathered at the time 

 of fertilisation, we may be able to follow individual pollen-tubes 

 to an oosphere. As longitudinal sections show, the pollen-tubes 

 penetrate to the embryo-sac through the conducting tissue of 

 the nucellus, growing in that direction in which they are best 

 nourished. The pollen-sac is thickly filled with small grains, 

 which iodine shows to be starch. In suitably fixed material 

 one can without difficulty see the reproductive cells of the pollen- 

 grain, and the vegetative nucleus, in the swollen end of the pollen, 

 tube. The reproductive cells are present to the number of two, 

 which have resulted from the division of their mother-cell. The 

 pollen-tubes attain to the embryo-sac, penetrate between the cells 

 of the neck, and thus to an oosphere, into which one of the two 



