and the Prothallns of Peranema cyatheoides , D. Don . 103 
becomes pushed out on the side at first uncovered by the indusium (Fig. 2) 
and may remain exposed until sporangia appear (Fig. 2). In some sori the 
indusium covers the receptacle entirely, even before the sporangia are fully 
defined (Fig, 3). 
As the sorus grows older, an elongation of the receptacle goes on 
(Figs. 3 and 5), the central part of the resulting stalk being continuous with 
the receptacle, and the peripheral part continuous with the indusium. The 
side of the indusium in Fig. 4 up almost to the £ kink ’ represents the portion 
which later becomes one side of the soral stalk (the portion up to the sharp 
bend below the start of the indusial flap in Text-fig. 1). The number of cells 
from side to side across the base of the sorus in Fig. 4 is exactly the same 
as the number across the stalk of the mature sorus in Text-fig. 1, while the 
number of cells from a to b in Fig. 4 corresponds with the number from a to b 
in Text-fig. 1. (A counting of the number of cells in length and width of 
the stalk of the sorus figured in Fig. 13, Ann. of Bot., xxvi, PL XXIX, gives 
precisely the same results. As this sorus was cut from another plant and 
the figure was made long before the material which forms the subject of this 
present paper was obtained, it is interesting to observe how closely the sori 
adhere to one type of construction. Comparison of herbarium specimens 
collected at wide intervals of time shows how constantly the sori preserve 
the same size and form.) The elongated condition of the cells of the stalk 
in Text-fig. 1 suggests what a comparison of Fig. 4 and Text-fig. 1 makes 
obvious, that, to produce the mature condition, there has been simply 
a lengthening of the cells at the base of the receptacle, and of the cells of 
the tissues which in the young sorus are continuous with the indusium. 
Apparently cell-divisions go on in the superficial layers of the young sorus 
until sporangia are initiated on the receptacle. Then a lengthening of the 
individual cells of receptacle and superficial layers produces the stalk of 
the mature sorus. 
The receptacle in the youngest stages examined has in tangential 
section the outline of an hour-glass. In median section it is shown curved 
at its tip towards the edge of the leaf (Fig. 1). It widens at its apex as it 
grows older (Fig. 3) ; its lower portion becomes constricted, its apex broadly 
dome-shaped (Figs. 4 and 5). The broad dome-shape is found in the fully 
developed sorus (Text-fig. 1). 
In even the youngest leaves which bear sporangia, the vascular tissue in 
the veins is defined. The young sorus is always produced below a vein, and 
the vascular tissue of the vein runs into the base of the sorus. In the earliest 
stages no tracheidal tissue is present in the upper portion of the receptacle or 
in the stalk (Figs. 1, 2, and 5), but the cells of the central series, particularly in 
the lower part of the stalk, become very much elongated, and are narrow even 
in a fairly young sorus (Fig, 5). When the stalk reaches its full length, the 
cells of its central region are more or less in process of change into tracheides ; 
tracheides are at the same time defined in the receptacle proper. In the 
mature sorus the tracheidal system runs as a narrow strip up through the 
