1883.] of the Field Horsetail. 13 
From this time on, the growth is very capricious; branches are 
given off, apparently without any definite order, the cells already 
formed also dividing, so as to make the prothallium broader and 
thicker. This growth continues until antheridia are to be 
formed. ; 
For two or three weeks the spores grown in water and in 
moist earth, develop in much the same manner, but finally those 
in water grow much less rapidly, though seeming to retain their 
vitality to some extent. Their growth is more erratic, many 
growing fora long time without dividing, forming single cells 
that are very much elongated; others develop without sending 
“out any root-hair, and nearly all, after three or four weeks, stop 
growing, or grow very feebly. When sown in water the spores 
soon sink and form a filmy green mass closely resembling a 
small alga. Those grown on earth form bright green, velvety 
masses that might readily be taken for a small moss. In both 
cases the long root-hairs, becoming entangled, make the pro- 
thallia cling together in great numbers where the spores are 
thickly sown. The abnormal development in water is probably 
Owing to the lack of proper nutriment as well as to the different 
physical conditions to which the spores are subjected. 
For a considerable time before antheridia were formed, the 
prothallia increased but little in length, but became noticeably 
broader and thicker, the ends of the main branches growing 
blunter and dividing up into short branches, so as to become 
somewhat club-shaped (Fig. 17). This process was slow at 
first, but after the first antherozoids were formed, there was a 
rapid increase in the size of the prothallium. 
The first mature antherozoids were observed June 7th, nearly 
six weeks from the time the spores were sown ; Fig. 20 gives the 
appearance presented by the prothallium at the time that the first 
antheridia are formed. Hofmeister gives five weeks as the time 
requisite for the production of the first antherozoids, but this dif- 
ference of a few days in the time, may be readily accounted for 
by the extraordinary lateness of the past spring. 
From the very great simplicity of the structure of the anther- 
idium, it is very difficult to say just when it begins to be formed, 
for it is merely an excavation or cavity in the end of a branch of 
the prothallium that becomes filled with protoplasm more dense 
than that in the body of the prothallium. After the mature an- 
