22 Lawson. — The Gametophytes , Archegonia , Fertilization , and 
The larger of these nuclei is the tube-nucleus, and the smaller, which 
is situated near the wall of the spore, is the generative nucleus. No trace 
of nuclei or cells representing the vegetative tissue of the male gameto- 
phyte were found. 
No further division of the nuclei in the pollen-grain takes place until 
the pollen-tubes are partially developed. There are usually three or four 
pollen-tubes present, and they pursue different courses. One or two of 
them may grow down between the nucellus and the integument for a 
considerable distance, while others penetrate the nucellus immediately at 
the apex. 
Just about the time the tube penetrates the nucellus the generative 
nucleus divides, giving rise to the stalk- and body-nuclei. 
The body-nucleus becomes very large, and surrounds itself with a zone 
of dense cytoplasm, which in turn is surrounded by a membrane. The 
tube now contains one large cell and two free nuclei. 
During the latter part of June the body-cell divides and gives rise 
to two male cells. At first the male cells are flat on one side but soon 
become spherical. They are of equal size and both are functional. 
There are from four to six macrospore mother-cells organized from 
centrally situated hypodermal cells of the macrosporangium. Each 
mother-cell divides twice, but one cell fails to develop into a spore, so that 
there are from eight to twelve macrospores formed. The first is the 
reduction-division which marks the beginning of the gametophyte. It 
takes place about the first of March. 
Each macrospore begins to germinate. Some of the spores enlarge 
more rapidly than others, but the enlargement is always accompanied by 
a nuclear division. Although of various shapes and sizes, each macrospore 
now contains two free nuclei. The majority of the sacs or young prothallia 
show no further development, but two or three of them grow very rapidly 
and extend down through the tissue of the nucellus in the direction of 
the chalaza. 
Of the two or three sacs that continue their growth, one develops much 
more rapidly than the other one or two. In the early stages of the 
prothallium there is a progressive and simultaneous division of the free 
nuclei. These are at first distributed throughout the length of a long 
central strand of cytoplasm. By the development of large vacuoles which 
eventually fuse together, the cytoplasm and the free nuclei are forced to 
the wall. The prothallium at this time consists of a very large central 
vacuole, surrounded by a parietal layer of cytoplasm in which the numerous 
free nuclei are distributed. 
As the prothallium increases, the nuclei divide rapidly and frequently. 
The cytoplasm and nuclei now accumulate in great abundance in the 
lower, and less so in the upper portions, and the vacuole is reduced 
