1888,] Dr A. B. Griffiths on Malpighian Tubules. 
403 
these crystals are treated with nitric acid, and then gently heated 
with ammonia, reddish-purple murexide is obtained, crystallised in 
well-formed prisms. 
Fig. 2. — Malpighian Tubules of x 230. 
A = Longitudinal section, showing the various states of 
the epithelium lining. 
B = Transverse section of tubule. 
(2) If a fresh Malpighian tubule is placed upon a slide under the 
microscope and crushed, then a drop of dilute acetic acid added and 
the whole covered by a cover-slip, rhombic and other crystalline 
forms are deposited. If the cover-slip is now raised, a drop of nitric 
acid and then ammonia added, on warming over a spirit-lamp and 
replacing the cover-slip, beautiful prismatic crystals of murexide 
are easily distinguished. 
(3) Ho other ingredient, besides uric acid, could be detected in 
the Malpighian tubules of Libellula depressa. 
From these reactions, it is right to conclude that the tubules 
represent the true renal organs of this species of the Heuroptera. 
7. On a Fungoid Disease in the Roots of Cucumis sativa. 
By Dr A. B. Griffiths, F.R.S. (Edin.), F.C.S. (Bond, and 
Paris), Principal and Lecturer on Chemistry and Biology., 
School of Science, Lincoln ; Member of the Physico-Chemical 
Society of St Petersburg, ^c. (Plate XVI.) 
A considerable amount of work has been performed in investigat- 
ing the nature of the nodular outgrowths upon the roots of various 
plants. One of the earliest observations in this direction was by 
