5/2 MB. D. H. SCOTT CS THE ARTICULATED 



by the " articulated " structure of their laticiferous tubes. It 

 must, however, be remembered that his so-called articulated 

 tubes are not vessels, but simply series of sacs of equal or of 

 varying length, the walls of which, according to his observations, 

 probably do not undergo absorption. Hence the inclusion of 

 Hevea in this division does not seem to be very strongly supported 

 by the anatomy of its laticiferous tissue ; though the removal of 

 the genus from the neighbourhood of JatropJia, which has quite 

 tvpical inarticulated laticiferous cells, certainly seems to be de- 

 manded if anatomical characters have any real weight in classifi- 

 cation. In support of Dr. Pax's view of the relationships of 

 Hevea, it may be urged that a transition from a system of closed 

 sacs to a network of true vessels is not difficult to comprehend ; 

 it has probably taken place both in the Papaveracere and Aroidese, 

 as will be further shown below. The difference between the two 

 forms of tissue is quite comparable to that between tracheides 

 and vessels ; and this is regarded by nearly all anatomists as of 

 secondary importance. Hence a near relationship between Hevea 

 and the Acalyphinece investigated by Dr. Pax, is at least not 

 opposed by the respective characters of their laticiferous tissue. 



A second point of difference between Dr. Pax's classification 

 and that given in the ' Genera Plantarum ' affects the position 

 of the genus Manihot. This is placed in the latter work in the 

 subtribe Adrianece. This arrangement is condemned by Dr. Pax, 

 who speaks of the genus as having been " incorrectly severed by 

 Bentham from the Jatrophea"* Dr. Pax accordingly places 

 Manihot next to JatropJia among his Hippomanece ; and this is a 

 tribe characterized in his arrangement by its inarticulated latici- 

 ferous tubes. It need hardly be said that my investigations here 

 tend entirely to confirm Bentham's conclusion, which may indeed 

 be regarded as a remarkable example of that instinct for affinities 

 for which the greatest systematic botanists are distinguished. Iu 

 the structure of its laticiferous system Manihot is as remote from 

 JatropJia as one plant can be from another. If such anatomical 

 characters are of any systematic importance at all (and Dr. Pax's 

 whole work rests on the assumption that this is the case), the 

 separation of Manihot from the Jatrophece must be regarded as 

 fully justified — quite as much so, in fact, as that of Hevea. 



Dr. Pax is disposed to regard the form of laticiferous tissue 

 which consists of a series of closed sacs (his " articulated tubes ") 

 as having given rise, in the phylogenetic development, to the in- 

 * i.e. p. 410. 



