674 Thoday.—On the Histological Relations between 
lysed products of the cellulose which is continually being absorbed by the 
parasite as it burrows through the cell-walls of the host. In this connexion 
it is interesting to notice the absence of granules in Cuscuta growing on the 
thin-walled Begonia , and their great number in the same species of Cuscuta 
growing on Salvia , with its thick-walled pith and pericycle. Heinricher’s 1 
examination of the smaller and more compact granules in Lathraea 2 led 
him to describe them as ‘ amylo-dextrin \ These granules have no very 
close resemblance to the more irregular masses in Cuscuta , and it is not 
known whether they stain with callus stains. They are present both in 
tracheides and parenchyma ; their reactions resemble to some extent those 
in Cuscuta. Both turn a darkish brown with iodine in potassium iodide, the 
colour fading later, and both lose their refractiveness on swelling. With 
sulphuric acid there is a great deal of swelling and degeneration into 
mucilaginous drops. 3 
It appears probable that the granules and masses thus occurring in 
so many parasite haustoria are at any rate of allied nature. In Cuscuta 
their absence at an early stage even when growing on Salvia suggests that 
at first all the cellulose dissolved by the ingrowing haustorium is needed by 
the parasite, and is converted into soluble form and translocated ; later, as 
the hyphae reach the functional phloem, and richer supplies of food are at 
their service, the hydrolysed cellulose is deposited in the form of these blue- 
staining granules and masses. Their accumulation at a later stage must to 
some extent choke the old haustoria. 
C. The origin of connecting threads . It has been suggested inde¬ 
pendently by Russow 4 and Kienitz-Gerloff, 5 and the view is strongly 
supported by Gardiner, 6 that the connecting threads found throughout 
plant tissues are present ab initio in the young cell-wall. Their origin 
is regarded as connected with the spindle fibres found between the 
dividing halves of the nucleus, which are so to speak ‘imprisoned in the 
young wall \ 7 
On the other hand Strasburger 8 remains the chief exponent of the 
view that connecting threads, though often appearing in the young tissues, 
owe their origin to the formation of ‘ plasmodesmic pseudopodia pro¬ 
cesses growing out from the protoplasm and boring through the young 
cell-wall. On this view the development of protoplasmic connexions need 
not be confined to genetically connected cells. 
It will not be easy to obtain direct developmental evidence such as 
would be conclusively in favour of either of these two views. To find 
1 Heinricher, 1894, p. 349, and 1901, p. 725. 2 Ibid., Fig. 7, PI. IX. 
3 Cf. Heinricher, 1894, pp. 343 ff. 4 Russow, 1883. 
5 Kienitz-Gerloff, 1891. 6 Gardiner, 1898 a, 1900, 1907. 
7 Gardiner, 1898a, p. no; see also Hill, 1908, pp. 2S2-3. 
8 Strasburger, 1901, pp. 493 ff. and 1902, pp. 52-3. 
