254 Hill ’ — The Histology of the Sieve-Tithes of A ngiosper ins. 
phenomena attendant upon the development of the various types of sieve- 
tube connexions throughout the vegetable kingdom into one harmonious 
series of events. 
It may be noted here that Strasburger says nothing further as to the 
character of the sieves in Conifers. 1 In the fourth edition of the ‘ Kleines 
Botanisches Practicum ’ the figures of the sieves of Pinus 2 have, as I 
have already stated, been altered, and the callus is represented as being 
pierced by fine threads, but whether he considers that the method of callus 
formation put forward in 1901 still holds, or whether the results of the 
paper on the histology of Pinus have altered his opinions, is not clear. With 
regard to the sieve-plate of Angiosperms the statement is made 3 that in 
consequence of my results with Pinus 4 a correction is necessary in the sense 
that slime-strings and not callus-rods are formed from the ‘ Plasmodesma 5 
or connecting- threads. How the acceptance of these results affects his views 
on the boring of the fields of the sieve-plate by one large central slime- 
string, when according to his new point of view the young field should be 
occupied by a group of slime-strings, 5 or how the callus which lines the pores 
of the sieve-plates is formed, is not stated. In the same way the character 
of the lateral thread groups is left in an unsatisfactory condition, for no 
explanation is given of the relation of the slime-strings to the callus, which 
was supposed to be formed by the swelling up of the free ends of the 
transformed protoplasmic threads 6 as in Conifers. 
Two other papers require a brief notice before closing this resume. 
Kuhla, 7 in his paper on the protoplasmic connexions in Viscum album , 
published in 1900, includes some account of the sieve-tubes of Cucurbit a and 
of Viscum. He worked with alcohol material of Cucurbita fixed by boiling, 
according to Fischer’s method 8 , and stained by Meyer’s Pyoktanin method. 9 
The points which he wished to settle are clearly stated in his paper, 10 but, 
though figures are given which purport to answer the questions propounded, 
there is reason for believing that the appearances figured do not, in most 
cases, really correspond to actual structures. 
In the first place the callus is neither mentioned in the text nor 
referred to in the figures, which therefore renders Figs. 8, 17, and 35, 
1 Strasburger, Bot. Zeit., lx, pp. 49-53. 
2 Bot. Pract., ed. iv, 1902, p. 86, Fig. 49 a and b, p. 85. In these two figures fine threads each 
with a dark median node are shown. In Fig. b there seems to be a suggestion of a median nodule 
enclosing the nodes, which does not appear in a. The figures, however, are so vague and indefinite, 
and there is so little allusion to them in the text, or to the fact that they differ from those previously 
published, that it is difficult to be certain about them. There is no proper explanation of Fig. 49 c, 
and it does not apparently harmonize with either a or b. 
3 Strasburger, B. Z., 1 . c., p. 52. 4 Hill, Ann. Bot., vol. xv, 1901. 
5 Cf. Strasburger, Pringsh. Jahrb., 1901, Fig. 32, PI. XIV, in the light of B. Z., 1902, p. 52, § 2. 
6 Strasburger, 1901, pp. 531, 532. 7 Kuhla, F., Bot. Zeit., 1900, p. 29. 
8 Fischer, 1886, Beit, zur Kennt. der Siebrohren, Leipzig. 
9 The Viscum material appears to have been fixed in 1 per cent. Osmic acid. 
10 Kuhla, 1 . c., p. 39. 
