174 Shiv Ram Kashyap.— The Structure and Development of 
It is very easy to distinguish the prothalli bearing antheridia. The 
folded margins, their red colour (deeper when the whole prothallus is red), 
their smoother surface, all indicate their presence. 
It is known that in other species of Equisetum it is possible to convert 
female prothalli into male by starving them, and as a rule the smaller and 
poorly nourished prothalli are male. What are the conditions which induce 
the formation of the antheridia when the prothalli of E. debile have been 
forming archegonia for some time was not determined experimentally. 
Other considerations, however, make it probable that temperature and age 
are the determining factors. In the first place only a few small prothalli 
were found even in December bearing antheridia, although small prothalli 
are very common at that time. In the latter part of December many small 
prothalli were seen with one or two plants growing out of them. As 
regards temperature, it will be seen from the following table that the tem- 
perature gradually falls from September onwards, and the lowest mean as 
well as the lowest mean minimum temperature is reached in December and 
January. 1 have to thank the officials of the Lahore Meteorological 
Observatory for the following figures : 
Temperature in 
Shade (Fahrenheit) at 
Diurnal range. 
Lahore for 
1912-13 
Sept. 
Oct. 
Nov. 
Dec. 
Jan. 
Feb. 
Mar. 
Mean maximum . 
. 100*2 
96.3 
80-7 
71*9 
73 -i 
70.4 
78-0 
Mean minimum . 
. 71*0 
60*5 
49.2 
42.7 
42*4 
48*7 
52.0 
Mean .... 
. 85*6 
78.4 
64.9 
57-3 
57-8 
59.6 
65.0 
Average monthly 
. 29-2 
35-8 
31.6 
29.3 
30*7 
21.8 
25-9 
Absolute maximum 
103-3 
103.4 
89*6 
77.6 
78*4 
76-3 
94.6 
Absolute minimum 
. 62.5 
55 -i 
38.6 
37 - 2 
36* [ 
39 -7 
45*2 
Development of the Antheridium. 
It is easy to follow the development, as antheridia in various stages of 
development are often found in the same vertical radial section (Figs. 31, 32). 
Each antheridium is developed from a single superficial cell which divides 
by a periclinal wall ; the upper cell contains a large number of chloroplasts 
in which the red pigment mentioned above is associated with the chlorophyll. 
These chloroplasts here as in other cells of the prothallus are often con- 
centrically arranged round the nucleus. The lower cell gives rise to the 
spermatogenous cells. It first divides by a periclinal wall, and later on 
periclinal and anticlinal walls are formed with considerable regularity. The 
spermatogenous cells have the same structure as described by Sharp, but 
plastids are not generally met with. One or more nucleoli are present in 
the nucleus as in all the cells of the prothallus. The outer cell divides once 
or twice, rarely oftener, by anticlinal walls and forms a roof of 2-4, or rarely 
more, cells (Figs. 34, 35). Dehiscence takes place by the separation of 
these cells (Fig. 34), which also bend outwards. The mature antheridia are 
