196 D. H. SOOTT. 



dermis and the buudle-sheath. Here the tubes themselves 

 have in many cases thick, collenchymatous walls. 



In the middle nerves of the three segments of the leaf, a 

 zone of laticiferous tissue extends all round the vascular bun- 

 dles, occurring inside the starch-sheath which here surrounds 

 them. Here, as in the petiole, a hypodermal system is also 

 present, which traverses the colleuchyma of the upper and 

 lower surface of the nerve. In the smaller veins of the leaf 

 the tubes accompany the vascular bundles on their lower side. 



In the young tetrarch or pentarch root the laticiferous 

 tissue is confined to the outer part of the four or five phloem 

 groups. It does not occur in the hypodermal position. 



In the thickened tuberous root the laticiferous tubes occur 

 in the secondary cortex, forming, together with the sieve- 

 tubes, a coarse network, enclosing the large medullary rays. 



I will now return to the secondarily thickened stem. On 

 examining transverse sections, the laticiferous tubes of the 

 phloem are seen to be very numerous. They appear to be con- 

 nected one with another in the tangential direction by trans- 

 verse branches, especially in the outer part of the phloem. The 

 observation of a tangential section through this region at once 

 shows that this is actually the case, and thus discloses the first 

 important difference between the laticiferous tissue of Manihot 

 and that of Euphorbia. The occurrence of anastomosis in the 

 latter has always been doubtfuL Schmalhausen,^ indeed, be- 

 lieved that it probably occurs in the nodes, young leaves, apex 

 of the root, &c., but De Bary ^ considers this questionable in 

 every case, and only admits its possibility as regards the nodes. 

 The most recent investigations are those of Schullerus,^ who 

 comes to the conclusion that, in E. Lathy ris at least, anasto- 

 mosis does not take place at all, either in the nodes or else- 

 where. Here, in the cortex of Manihot, anastomoses are 

 extraordinarily frequent, and often very regularly arranged. 



* 'Beitr. z. Kentniss d. Milchsaft-behalter d. Pflauzen,' St. Petersburg, 

 1877. 



* L. c, pp. 199, 205. 



« 'VerhancU. d. Bol. Vereins d. Prov. Braudenburg,' 1882, 2, p. 92. 



