450 Messrs Gardiner and Hill, The Histology 



the accompanying group of threads presents the appearance of the 

 so-called "pit-threads 1 " — "aggregirte Plasmaverbindungen " — on 

 the one side, and of the " wall threads " — " solitare Plasmaverbind- 

 ungen " of Kohl 1 — on the other side of the middle lamella, and it 

 is therefore clear (and this is also true for the endosperm of 

 Phoenix) that the distinction which has been made between these 

 two forms of threads in thick- walled endosperms is not a valid one, 

 since all gradations from the " pit " type to the " wall " type may 

 occur in the endosperm tissue of one and the same seed. 



The composition of the reserve cellulose in Galium as in Tamus 

 is rather a matter of conjecture. Yet sections of the fresh endo- 

 sperm give fairly definite results, which tend to prove that the 

 walls are composed of a substance of the nature of pecto-cellulose. 

 With weak watery methylene blue, all the walls take up the stain, 

 but those just under the testa stain more deeply. With Congo 

 red, on the other hand, all the walls are stained pale pink, with the 

 exception of those just beneath the testa, which are scarcely 

 coloured by the stain, and a similar effect was also noticed with 

 a solution of iodine in potassium iodide. On treating sections 

 with iodine and sulphuric acid the cell walls turned a bright 

 greenish blue. 



If sections of a seed which has been allowed to germinate are 

 examined, it is seen that the space occupied by the cotyledons has 

 become considerably enlarged, and the endosperm cells lying 

 around this cavity have become somewhat crushed and depleted of 

 their contents. The walls of the cells also in this region appear 

 thinner and more mucilaginous than those situated at a greater 

 distance from the developing embryo. In sections treated with 

 methylene blue or Congo red these differences are very sharply 

 marked, for with the blue the cells around the cotyledonary cavity 

 remain uncoloured, whereas the walls further away are fairly 

 deeply stained, but with Congo red, on the other hand, the walls 

 of the cells which surround the cavity, and which appear mucila- 

 ginous, stain a deep rose-pink, whilst those which are as yet 

 unaltered only take on a faint pink coloration (Fig. 12). Similar 

 effects to these were noticed in sections stained in safranin, and 

 in this case the mucilaginous walls are unaffected by the stain. 

 From such results it seems highly probable that the composite 

 cell walls are being disorganised by an enzyme in such a way that 

 the pectic compounds, which were seen to stain with methylene 

 blue or safranin in the ungerminated seed, are being removed, 

 whilst a matrix, consisting of an hydrated form of pure cellulose, 

 which gives the characteristic reactions with Congo red and iodine 

 and sulphuric acid, is left behind. 



1 Kohl, " Dimorphism us der Plasmaverbindungen," Ber. d. Deut. Bot. Ges., 

 Bd. xviii., 1900, p. 364, Taf. xn. 



