NOTES. 
ON THE APICAL GROWTH OF FUNGAL HYPHAE.— It is usually 
stated in the text-books (e.g. Gwynne-Vaughan (1), p. i) that the growth of fungal 
hyphae is apical, and it is obvious that the greater part of the elongation does take 
place at the tip. One might, however, reasonably expect that some extension of 
the more recently formed segments also occurs, and that growth, while mainly apical, 
is also to some extent intercalary. I have been unable to find any published account 
of detailed observations maintained for any considerable period of time, and, as the 
question is of importance in connexion with rates of growth, a brief record of some 
experiments ad hoc may not be superfluous. 
Spores or, in some cases, fragments of mycelium were sown on the surface 
of miniature agar plates, formed by pouring agar on cover-slips, 1 which were then 
inverted over van Tieghem cells and the preparations incubated at 24°-25°C. After 
germination had occurred and the hypha had reached a convenient size, the lengths 
of the segments already formed were measured, at varying intervals of time, over 
a period extending in different cases from five to fifty-six hours. Where septa were 
absent or difficult to distinguish, the intervals between successive branches were 
determined. The agar used was a batch of clear prune agar, and the observations 
were made at room temperature. Measurements were made with a Bausch and 
Lomb screw-micrometer eyepiece and Zeiss C objective. 
It is unnecessary to give a detailed account of the observations with the different 
organisms examined, but abbreviated records of two experiments may be given 
as examples. 
J Table I. 
Fusarium No. 18. (Prune agar : measuremefits in g ; times in minutes 
from the first measurement .) 
Time 
0 
100 
161 
249 
323 
4°7 
489 
1468 
Segments 1-7 
494.9 
496.6 
499.6 
497.6 
497-6 
499-3 
498-6 
496.7 
Segments 8 
23*3 
23-3 
23-3 
23-3 
2 3-3 
23-3 
23-3 
Segments 9-11 
143-3 
140.9 
i4i-3 
I 4 1 '7 
I43-3 
140.4 
138-3 
„ 12-14 
j 38-7 * 
138.4 
137-3 
135-9 
1 37*7 l 
O 
9 
„ 15~ 1 7 
162.3 
161-7 
158-7 
161.6 \ 
„ 18-21 
163-0 
162.7 
163-3 
163.6 
»> 22-25 
305-9 
306.9 
3°5- 6 
To tip 
186.7 
206-7 
190-0 
200-0 
i 83-3 
70-0 
235*0 
2334-0 
Whole hypha 
681.6 
869-9 
99 2 \5 
H62.9 
I307-9 
I 499- 1 
1 704-5 
3762-2 
Table I shows the result of an experiment with Fusarium No. 18. When first 
measured the hypha showed seven segments or cells, which together measured 
494-9 [a, and the length between the tip and the nearest septum was 186-7 g. As the 
1 This may be done very conveniently by laying on a cover-slip a glass ring, such as is used in 
a van Tieghem cell (it must not be too small—1.7 cm. is a convenient size), and pouring into 
it melted agar to any desired depth. When the agar has set the ring is removed and leaves 
a circular platform of agar, which after inoculation is laid on the cell in the usual way. Ihe 
growing organism is easily observed through the agar. 
(Annals of Botany, Vol. XXXVII. No. CXLVI. April, 1923.] 
