104 
B. Muriel Bristol. 
filaments often assume a strong spiral twist within the mucous 
sheath, points of reversal of the spiral being very conspicuous. 
The vegetative cells are barrel-shaped, about as long as they 
are broad, and the end cells are conical. The heterocysts are 
spherical or occasionally oval and of a yellowish colour ; they may 
form short series of two or three together. The spores lie either 
singly or in pairs, generally on both sides of the heterocysts, but 
they differ from the typical form in being almost invariably oval 
and very much broader in proportion to their length. When ripe 
the walls of the spores become yellowish-brown in colour. 
Two forms of this variety have been observed, differing from 
one another only in size : 
(a) forma minor. 
From the old stored soils this form has been observed in 
the cultures of only one sample, Broadbalk 1865, but it has also been 
obtained from five recently dried soils, and is therefore probably to 
be regarded as the more usual form. 
The vegetative cells are generally 2-5-3-5/a broad though they 
may occasionally be as much as 4/a ; the heterocysts are about 
4-5 /a in diameter and the spores are 9-10/a broad by 13—17/x long. 
In this old soil it has retained its vitality for fifty years. 
(b) forma major. 
This occurred in the cultures of the 1893, 1869 and 1856 
samples of the Broadbalk soil, but has not been observed in any 
of the recently dried soils. The vegetative-cells are usually 4-5 /a 
in diameter, occasionally a little less; the heterocysts are 5-7/a in 
diameter, and the spores 11-12-5/a broad by 15-19/a long. 
It germinated after a resting-period of fifty-nine years. 
Nodularia Harveyana (Thwaites) Thuret. 
[= Nodularia turicensis (Cramer) Hansg.] 
This species was obtained from the 1846 Broadbalk sample 
and is interesting for two reasons. In the first place it shows, 
more than any other alga except Nostoc muscornm, an extra¬ 
ordinary power of retaining its vitality, having germinated after 
nearly seventy years extreme drought. 1 The absence of this 
species from the later Broadbalk soils must therefore probably 
' The first record of longevity in algae was made in connection with this 
species; and it was this observation which led Professor G. S. West to 
suggest the present investigation.— Vide West, Algae, Cambridge Botanical 
Handbooks, Vol. 1, p. 28, 1916. 
