LATICIFEEOUS TISSUE OP MANIHOT GLAZIOVII. 201 



well. I have measured secondary sieve-tubes with a diameter 

 of 'OSl, *035j and '04 mm. respectively. The former dimensions 

 are more usual. The sieve-tubes are accompanied by narrow 

 companion-cells with the typical characteristics. In the pri- 

 mary sieve-tubes of the younger portion of the stem I have 

 occasionally found nuclei. The members of the sieve-tubes 

 seem to be multinucleate, as in one case at least I have 

 counted three nuclei in a single element. 



As regards the relative positions of the laticiferous tubes and 

 the sieve-tubes^ no very strict regularity prevails. Generally 

 speaking, they form alternating concentric rings. As many as 

 three sieve-tubes may occur in contact in the same radial row. 

 Laticiferous tubes and sieve-tubes are very commonly sepa- 

 rated by a single cell of the phloem-parenchyma. In a few 

 cases I have found actual contact between the two. 



As regards the occurrence of nuclei in the laticiferous 

 vessels, I have not found ]\Ianihot Glaziovii to be an espe- 

 cially favourable object for investigation. The presence of 

 nuclei in the transverse connecting branches is easy to deter- 

 mine, but I have not often succeeded in demonstrating their 

 presence in the main longitudinal trunks. I have found chlo- 

 roform a useful reagent in this investigation, as it dissolves out 

 the caoutchouc forming the bulk of the latex. The sections 

 are transferred from absolute alcohol to a test-tube containing 

 chloroform, in which they are shaken up and then left for 

 about half an hour. They are then washed in absolute alcohol. 

 The latex is found to have practically disappeared. In some 

 cases I have been able to find traces of protoplasm and small 

 nuclei in such preparations on staining with hajmatoxylin, but 

 in others the tubes appear to be quite empty, so that the 

 constant presence of a living protoplasmic body in the mature 

 vessels would seem to be questionable. I should be sorry, how- 

 ever, to lay any weight on purely negative results, and this 

 question must be reserved for renewed investigation. 



I have made a general investigation of the laticiferous tissue 

 in M. utilissima and M. Aipi, and have found it to agree 

 1 Cr. Russow, 'Dorpater Naturforscber Gcsellschaft,' 1SS3, p. 282. 



