132 



BOTANY 



closely resemble in their structure the unilocular sporangia of the Kelps. The 

 nucleus of the young antheridium divides repeatedly, and there follows a divi- 

 sion of the cytoplasm into as many parts as there are nuclei. The spermatozoid 

 (H) has a large nucleus and an orange -red pigment-spot, so that in mass the 



antheridia have a decided 



A. orange color. This color 



makes it easy to recognize 

 the male plants in the dioe- 

 cious species. 



Oogonium. The oogo- 

 nia are very much larger 

 than the antheridia, and 

 when ripe are of a dark 

 olive-green color. They 

 arise directly from the cells 

 forming the wall of the 

 conceptacle and not from 

 the hairs. The mother-cell 

 of the oogonium divides 

 into a basal cell and a ter- 

 minal one, which ic the 

 oogonium proper. At first 

 the cell is colorless, but it 

 becomes opaque and filled 

 with olive-green or brown 

 chromatophores as it devel- 

 ops. The nucleus divides, 

 probably in all cases, into 

 eight, and this is followed 

 by a division of the cyto- 

 plasm, usually into as many 

 parts, but in some species into a smaller number (i.e. two in F. fastigiatus) . In 

 Halidrys there is but a single egg in the oogonium. In all the forms that have 

 been thoroughly investigated, the nucleus divides into eight, whether the full num- 

 ber of egg-cells is formed or not, the superfluous nuclei becoming disorganized. 



Fertilization. When ripe, the reproductive organs are easily 

 broken away, and when exposed to the water, which happens in 

 those forms growing between tide-marks when the tide rises, the 

 wall of the oogonium or antheridium is dissolved, and the reproduc- 

 tive cells are gradually set free in the water. The minute sperma- 

 tozoids have two laterally inserted cilia, one being often longer than 

 the other. They collect about the eggs, and sometimes in such 

 numbers that the egg is made to rotate by the movement of their 

 cilia. A single spermatozoid only succeeds in penetrating into the 

 egg, where it fuses with the nucleus (Fig. 104, J). The egg is then 

 invested with a membrane, becomes pear-shaped, and attaches itself 

 by the pointed end. Cell-division now proceeds rapidly, and in time 

 an apical cell is established, but the details are still not quite clear. 

 The attached end forms a holdfast, and the upper part develops 

 into the branched thallus. 



FIG. 103. Fucus evanescens. A, growing-point of a 

 dividing shoot ; x, x, apical cells of the new shoots. 

 B, cross-section of the growing-point; x, the apical 

 cell (X 450). 



