Hill. — - The 'Histology of the Sieve- Tithes of A ngio sperms. 255 
PI. Ill, inaccurate. His figure (Fig. 10) of the threads between a sieve- 
tube and a cambiform cell in Cucurbita is also inaccurate for the same 
reason, since callus is always present in the sieve-tube side of these pit- 
closing membranes. Connexions between the sieve-tubes and the com- 
panion cells of Cucurbita are figured in Figs. 7 and 9, but these two 
figures are very different in character, and Fig. 7 corresponds very closely 
with his Fig. 8, which represents a sieve-plate 1 . It seems possible, therefore, 
that these thick threads may really be the stained pit fillings in the 
narrow paired pits of the companion cell-wall which have become narrowed 
by the swelling of the wall owing to the nature of the treatment to which 
the tissues have been subjected. 2 Even if the threads in Fig. 9 are real 
threads, the swollen state of the wall has produced a highly artificial effect. 
With regard to the presence of threads between the other tissues of the 
phloem, there is no doubt that they exist ; Kuhla’s figures of these are, 
however, unsatisfactory, and this is largely due to the great swelling of the 
wall and to the unsatisfactory and misleading nature of Meyer’s method as 
a method for research. 3 
Fig. 35 appears to have no adequate reference in the text 4 ; although 
it purports to be a very young sieve-plate, it is, I think, without doubt an 
old and empty plate with the sides of the pores stained by Pyoktanin. 
Kuhla's results with the sieve-tubes of Viscuni are worthy of more serious 
consideration and will be referred to again later, but it is as well here to 
point out certain errors of observation. In the first place the end-wall or 
sieve-plate of Viscum 5 is provided with callus, like that of the sieve-plates 
of other plants, and is pierced by slime-strings. Also, owing to the swelling 
of the walls, the very numerous pits in the side walls of the sieve-tubes have 
been entirely overlooked, and the threads are drawn with a regularity 
foreign to their normal distribution. 6 7 Nevertheless it should in all fairness 
be stated that the long walls between the sieve-tubes and the companion 
cells and between two adjoining sieve-tubes are filled with threads somewhat 
after the manner he has indicated. 
A few remarks about sieve-tubes are made by Kienitz Gerloff 7 in his 
recent paper, and a figure of a sieve-plate of Gagea lutea is given, but no 
callus is indicated, and there is nothing further on this subject in his paper 
which need claim our attention. 
It is possible that certain general statements made in the preliminary 
1 Cf. Kuhla, Bot. Zeit., 1900, p. 40. 
2 Ibid., p. 40; Eau de Javelle and Chlor-Zinc-Iod. appear to have also been used on the same 
sections ; cf. Fischer’s results, v. p. 248. 
3 For the above reasons and from my own results with Viscum obtained by other methods I am 
inclined to think that Kuhla’s elaborate numerical calculations may not be thoroughly reliable. 
* Perhaps p. 41 at the foot refers to this Figure. 5 Cf. Kuhla, 1 . c., Fig. 17. 
6 Kuhla, 1 . c., pp. 42 and 43, Figs. 12-14 ; cf. Hill, Fig. 26, PI. XVII. 
7 Kienitz Gerloff, Ber. der Deut. Bot. Ges., xx, 1902, p. 108. 
