62 



original tubercle into a shoot. He also made some observations 

 on the germination and the formation of the root of Viscum ; 

 but the observations of Du Hamel, Gaspard, and many others 

 have left little unknown on this subject. M. linger has how- 

 ever observed in several tropical species of Loranthus, that the 

 roots having a horizontal direction are not fixed in the bark 

 but on it, intimately surrounding the branches, and even ad- 

 hering to them with their extremities. 



In a second part, M. Unger gives his anatomical observa- 

 tions on the parasites, whose mode of insertion into the stock 

 plant has been previously described ; he concludes, that the 

 whole of the parasitical plants may be divided in a system- 

 atical point of view into three sections. The first comprises 

 those parasites, whose imperfect vascular bundles, having for 

 prototype Langsdorfia, are arranged in a circle and are con- 

 nected with each other by anastomoses. This section is placed 

 parallel with the formation of the stem in Ferns. A second 

 group is formed by those parasites in which the vascular bun- 

 dles are also imperfect, but in which it appears that a periphe- 

 rical formation of roots is added to that at their apices. This 

 section comprises the genera Orobanche, Lathr&a, Monotropa, 

 Cuscuta, Cassytha ; and M. Unger thinks that these plants, 

 with respect to their anatomical structure and mode of growth, 

 can be compared with none of the larger vegetable divisions ; 

 while the genera Viscum, Loranthus, &c. belonging to the third 

 section possess perfect vascular bundles and resemble dicoty- 

 ledons in their mode of growth. 



This mode of subdividing parasitical plants will probably 

 meet with little acceptation ; in fact I am not acquainted with 

 anything from which it can be proved that Orobanche, Lathraa, 

 Monotropa, Cuscuta, &c. differ essentially in their structure 

 and growth from other dicotyledons. It is true that Rafflesia 

 and Brugmansia exhibit a similar deposition of ligneous bun- 

 dles, or vascular bundles as they are here termed, on one an- 

 other, as in ferns ; but I can also produce stems of Cactus, in 

 which something similar occurs ; and therefore the drawing 

 an analogy between the genera of parasitical plants and ferns 

 cannot be justified. M. Unger thinks that his views on the 

 arrangement of parasites are strengthened from the structure 

 of their seed ; this supposition is however quite as erroneous 



