The Histology of the Sieve Tubes of Pteridium aquili- 
num, with some Notes on Marsilia quadrifolia and 
Lygodiumdi chotomum. 
BY 
E. M. MARGARET HUME, 
Bathurst Student of Newnham College , Cambridge. 
With Plates LIV and LV. 
N O re-examination of the sieve tubes of any Vascular Cryptogam has been 
made since more accurate methods of histological investigation have 
been introduced. It seemed therefore desirable to make an examination 
which would render possible a comparison between the sieve tubes of some 
Vascular Cryptogam and those of certain Angiosperms 1 and of Pinus , 2 as 
worked out by A. W. Hill, and of Macrocystis and Laminaria , 3 as worked 
out by M. G. Thoday (Sykes). 
Historical. 
De Bary 4 in his 4 Comparative Anatomy of Phanerogams and F'erns \ 
seems to have been the first to recognize the parietal layer of protoplasm 
which forms the characteristic lining of the sieve tubes of Vascular Crypto- 
gams. He also noticed that the refringent granules contained in the proto- 
plasm were aggregated against the sieve plates, and figures 5 a connexion 
between granules of adjacent sieve tubes, across the pit-closing membrane. 
De Janckzewski 6 also mentions the presence of the refringent granules, as do 
most persistently all writers upon the subject. He mentions that starch is 
very rarely present in the sieve tubes of either Vascular Cryptogams or 
Monocotyledons ; the latter, he says, also possess the refringent granules. 
He recognized that portions of the pit-closing membrane in Pteridium 
aquilinum give the same reactions as the callus of Angiosperms, but he 
regarded it as quite exceptional among Vascular Cryptogams, and held that 
their sieve plates are really unperforated. 
Russow 7 confirmed de Janckzewski’s observation of the presence of re- 
fringent granules in Monocotyledons. His examination of Vascular Crypto- 
1 Hill (’08). 2 Hill (’01). 3 Sykes (’08). 
4 De Bary (’84), pp. 180-2. 5 De Bary, loc. cit., Fig. 79 b. 
6 De Janckzewski (’82), pp. 59-65. 7 Russow (’82), p. 207. 
[Annals of Botany, Vol. XXVI. No. CII. April, 1912.I 
