ON BITTER CASSAVA. 109 



tissue, as "well as the rest. It is evidently a simple metamorphosis of the 

 tunica, which itself is a modification of the fleshy part. The tunica con- 

 sists of hexagonal cells, interspersed with elongated parallelogrammatic 

 cells, with comparatively few and very small starch granules, on some of 

 which a hilum could he distinguished. This tunica contains also lacti- 

 ferous vessels, which discharge a thick, white milk, similar in consistency 

 to that from the ruhher-tree. This milk presents also the characteristics 

 of rubber to some degree, after having heen exposed to the atmosphere for 

 some time. The interior or fleshy part of the root is composed of elon- 

 gated cells, which are perfectly crowded with starch -granules. Many of 

 the granules have a hilum, which is one, three, four, and six-cleft, the 

 latter description heing rare. Most granules have a perfectly circular cir- 

 cumference : some, however, are plano-convex, others angular, forming 

 trapezoids, and irregular pentagons and hexagons. It is surprising that, in 

 several works in which the starch-granules of hitter cassava are described, 

 no mention is made of the existence of a hilum similar to that of the rye- 

 starch granule. Is it possible that the Brazilian cassava is a different 

 species from ours ; or is there a mistake as to the identity of the starch ? 



The first quantitative determinations were mainly undertaken to 

 ascertain approximately the proportions of the three parts of which the 

 root consists. The weights were determined with the greatest accuracy ; 

 hut, of course, the proportions must vary from one root to the other. The 

 section of a small root gave the following proportion between the tunica 

 and the fleshy or central part: — Tunica weighed 1*863 grammes; fleshy 

 centre, 10*978. Which gives the proportion of 10 : 59. 



Second Determination. 



"Weight of the whole root 118*734 grammes. 



„ „ cuticle (not dried) 2*570 „ 



„ „ tunica 14*966 „ 



The starch determination was lost by accident. 

 "Weight of fibrous residue, exclusive of tunica... 11*953 grammes. 

 Proportion of tunica to fleshy centre, as 10 : 68. 

 Calculated for 100 parts, we have — 



Cuticle (not dried) 2*16 per cent. 



Tunica „ „ 12*61 „ 



Fibrous residue (dry) 10*07 „ 



Proportion of cuticle to tunica, as 10:58 „ 



Proportion of cuticle to both tunica and fleshy centre, as 10 : 452. 



Analysis of a small Fusiform Root. — No. I. 



"Weight of the entire root 291*903 grammes. 



Volume of the same 252 cubic centimetres. 



Specific gravity, therefore 1*158 



