14 Lawson . — The Gametophytes , Arckegonia , Fertilization , and 
above, one or two of the secondary prothallia have continued their growth, 
but at a much slower rate. Previous to the formation of the cell-plates, it 
is difficult to distinguish between the primary and the secondary prothallia, 
but after free cell-formation has ceased in the primary prothallium, the 
form of the secondary prothallium becomes well defined. Its course is long 
and tortuous, and in many cases winding in and out through the tissue of 
the primary prothallium, as illustrated in Fig. 18. Its shape is greatly 
modified, as its growth is limited to the spaces left by the more rapidly 
growing primary prothallium. Instead of having a single large vacuole 
and a parietal layer of cytoplasm, several long narrow winding vacuoles are 
present, separated by strands of cytoplasm. In several cases the spindles 
were found, showing that nuclear-division is carried on in the same manner 
as in the primary prothallium. In no case, however, was there any trace of 
cell-plate formation observed, so that I am inclined to believe that the 
secondary prothallia never develop sufficiently to produce cellular pro- 
thallial tissue. 
A very interesting relationship between the primary and secondary 
prothallia was noticed, which no doubt explains the sluggish development 
of the latter. After the cell-plates were formed in the primary prothallium, 
the parietal protoplasm of the secondary prothallium clings very closely to 
the cells of the former. These cells grow out into the free protoplasm and 
evidently act as absorbing organs. This intimate relationship is shown in 
Fig. 39. Here the newly formed cells are seen projecting into the proto- 
plasm of the secondary prothallium in a dovetail fashion. The nuclei of 
these cells are very much larger than the others, and have the appearance of 
being engaged in very active metabolism. There is no doubt that these 
projecting cells absorb the protoplasmic substance of the secondary pro- 
thallium, and thus retard its development. 
The primary prothallium of Sequoia takes just about three months to 
mature. The macrospores are formed during the first week in March, and 
the first archegonial initials were observed in material collected June 8. 
At this latter date the nucellar tissue had been almost completely absorbed, 
little more than the epidermal layer of cells remaining. Within the 
integument we now have a most confusing complex of structures, for in 
addition to the primary cellular prothallium there are usually present one 
or two secondary prothallia in an advanced stage of development and three 
or four pollen-tubes. 
The Archegonia. 
Very soon after the nuclei of the endosperm have been shut off from 
each other by the cell-plates, and after true cellular prothallial tissue has 
been organized, certain cells in the upper half of the prothallium become 
differentiated into the archegonial initials. These cells are quite numerous, 
and occupy a position not at the periphery, but near the central axis of the 
