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very close together ; one from the bank of a brook flowing with a 
fairly rapid stream thus keeping the plants always very moist ; the 
other collected a few rods away from a shallow ditch beside the road 
leading down over this brook. Here the soil to outward appearances 
seemed dry and the plants were small and in every way apparently 
much less developed than the more luxuriant ones by the edge of 
the brook. 
Such a difference there proved to be as can be seen from an ex- 
amination of the accompanying figures. Figs. 25, 26, 27b represent 
longitudinal sections through the tip of the thallus from plants gath- 
ered on the seemingly dry soil of the roadside ditch. Figs. 25 and 30 
show the earliest stages of the archegonia, the superficial cells just 
pushing out beside the growing point. Fig. 16a is the one-celled 
stage and fig. 16b shows a young archegonium which has divided to 
form a basal cell and the archegonium mother cell. The presence of 
the two nuclei indicates that a new cellwall was about to be formed 
thus dividing the archegonium mother cell into two cells by means of 
a vertical wall. Fig. 27b is a more advanced stage. Here the in- 
volucre which develops as soon as the archegonia appear begins to 
show and the archegonia are more advanced. In this illustration the 
central cell is seen to have been differentiated from the outer cells 
forming the wall of the archegonium. Fig. 28 represents the most 
advanced specimens of this material ; in this the central cell has di- 
vided into two parts, an upper one, which by division will form the 
neck canal cells, and the lower, which will divide into the egg cell 
and the ventral canal cell. In contrast to this material that gathered 
by the brookside presented the greatest variety of stages, from the 
earlier ones (Fig. 18) in which the archegonium mother cell has un- 
dergone its first division into two cells, through those in which the 
central cell has been differentiated from the outer cell (figs. 19 and 
20, to fig. 24) showing a full grown archegonium with sixteen canal 
cells. An average section through this material is shown in Fig. 27a. 
Here many of the archegonia seem to be fully grown and the pro- 
tecting envelope above and below has reached its full development. 
A comparison of these figures is a conclusive proof of the statement 
made earlier in the paper that plants growing in most situations are 
much farther advanced at the same season than those of a drier 
habitat. 
On June 20 the original collecting ground was returned to. Here 
unfavorable conditions due to the receding of the water and a thick 
growth of weeds and small shrubs had greatly reduced the PelUa 
colony and had apparently made the plants somewhat backward as 
they showed no advancement over those gathered from another local- 
ity on June 14. Sections of this material show exactly the same 
stages as those figured for that date. The archegonia are of varying 
stages, but have on the whole more of the later than the earlier ones. 
