34 2 
Notes. 
hypba grew, new septa were laid down, forming new segments. Every segment was 
measured separately, but, to economize space, adjacent segments are grouped together 
in the table. 
It will be seen that during the period of observation no change takes place in the 
length of the segments after they are once formed. The measurements vary a little 
owing to the difficulty of every time bringing the comparatively broad cross-line 
of the micrometer exactly in the same place over the septum, and also owing to the 
fact that the hypha does not grow perfectly straight. These discrepancies are 
experimental, and would have been reduced had the camera lucida been employed. 
There is no evidence of increase in the length of a segment, once it is formed, 
although the whole hypha had grown over 3,000 /x. 
The average length of the segments is 58*8 /x, and the distance from the 
nearest visible septum to the tip varied at the different observations from 70 to 260 /x, 
with an average of 191*5/x, the length of about 3-^ segments. Each septum is 
no doubt laid down some time before it becomes visible : how much before it is not 
possible to tell exactly. The whole hypha elongated at a mean rate of 2*1 /x per 
minute during the first eight hours, so that it would require about ninety-five 
minutes to increase by the length of 3-! segments. The elongation must occur 
in the portion between the tip and the nearest septum. It is, however, occasionally 
possible to get a measuring point much nearer the tip than the nearest visible septum. 
Branches may, and often do, arise from segments long after they are first formed ; but 
sometimes a branch is begun immediately behind the tip, and its bud is perceptible 
very close to the extreme tip. In such cases the interval between the point of origin 
of the branch and the nearest septum then visible remains constant, showing that 
elongation is taking place only at the apex, and not at all in formed portions of the 
hypha. 
A similarly abbreviated record of an experiment with Pyronema confluens is also 
given: see Table II. Here also the growth is entirely apical, the apparent small 
extension of the segments being probably due to errors of measurement, and in any 
case so very slight as to be negligible in comparison with the growth at the tip. 
Table II. 
Pyronema confluens. 
Time 
0 
66 
152 
263 
33 ° 
4*7 
476 
1469 
Segments 1 and 2 
25.1 
26.2 
25.8 
26.2 
26-9 
27*3 
27-0 
25.1 
Segment 3 
15*7 
16-4 
16.4 
16.8 
i 5 .° 
14.2 
16-1 
16.5 
Segments 4-6 
73-4 
75*3 
76-0 
74*9 
75*7 
Segment 7 
47*2 
48.0 
47*9 
>> 8 
48*0 
Segments 9-19 
5 l8 * 6 
To tip 
109.2 
137.2 
149.6 
127.5 
177*3 
190.5 
239.2 
420.0 
Whole hypha 
150.0 
179.8 
191.8 
244.1 
2 94*5 
355*2 
405.2 
11 5 1- S 
The following organisms have been examined similarly, and all show the same 
thing, that growth in length is exclusively apical. When septa were difficult to see, 
the intervals between successive branches were measured. 
Phytophthor a parasitica (Strain: Egg-plant, Nat. Coll. Type Cultures No. 1187). 
No change in intervals between branches in 22 hours ; hypha grew 389 /x. 
