LATICIFEROUS TISSUE OF MANIHOT GLAZIOVII. 195 



form character throughout each natural order. My observa- 

 tions on the genus Manihot show that the Euphorbiacese form 

 an exception to this rule. I have been able to prove that in 

 Manihot the laticiferous tissue consists of vessels, while in 

 the members of the order previously investigated it only occurs 

 in the form of the most typical laticiferous cells. The subse- 

 quent note on Hevea will show that the former structure is 

 not confined to one genus, but also reappears elsewhere in the 

 order. The laticiferous tissue of the Euphorbiaceae, except in 

 Euphorbia itself, is so little known that further researches may 

 not improbably disclose other important variations. 



It will be desirable in the first instance to give a general 

 account of the disti'ibution of the laticiferous tissue in the dif- 

 ferent parts of the plant. All the following statements refer 

 to M. Glaziovii (the species which I investigated most com- 

 pletely), except where otherwise stated. 



In the young stem, 3 mm. or less in diameter, at the com- 

 mencement of secondary thickening, the laticiferous tubes 

 form two series. One, which is much the less developed of the 

 two, is hypoderraal,^ occurring in or about the third layer from 

 the epidermis. The other series lies in the ring of bundles, 

 from four to six layers of cells within the bundle- sheath, which 

 is here "compound,'^ consisting partly of sclerenchymatous 

 fibres, and partly of cells which contain klinorrhombic and 

 clustered crystals of calcium oxalate, and which subsequently 

 undergo sclerosis. The inner system of laticiferous tubes is 

 continuous all round the stem, occurring in the interfascicular 

 tissue as well as in the phloem of the five primary bundles of the 

 internode. As secondary thickening goes on in the stem, 

 additional concentric series of laticiferous tubes successively 

 appear in the secondary cortex. 



In the petiole, besides the laticiferous tissue in the phloem 

 of the bundles, there is also a hypodermal system traversing 

 the thick layer of collenchyma which lies between the epi- 



^ This is meutioned by Trimen. See 'Report ou Progress, &c., of the 

 Royal Gardens, Kew,' for 1881, p. 14. 



