714 



may use the terra. Their vegetative functions go on unseen within 

 the substance of the plant infested by them, until the time arrives for 

 the performance of one grand object of their existence, the propaga- 

 tion of their kind ; the organs of reproduction then break through 

 the epidermis of the infected plant, just in the same way as the young 

 flower-buds of Kafflesia penetrate the cortical layers of the vine : the 

 spores of the parasite being perfected, are at length dispersed, and 

 having found a fitting nidus, a new generation goes through the 

 same round of operations as those which characterized the career of 

 its parent. 



But in most cases of parasitism among the phaenogamous plants, 

 the parasites seem invariably to act on their victims from without 

 inwards, that is, having fixed themselves on the external part, their 

 radicles gradually penetrate the tissue of the internal portion to a 

 greater or less depth. This is equally the case with Viscum and Lo- 

 ranthus, the seeds of which germinate on the bark of trees to which 

 they have previously been firmly attached by means of their own vis- 

 cid coating, and with Cuscuta, whose seeds in the first place germi- 

 nate in the soil; the young Cuscuta subsequently attaches itself to its 

 nurse by means of suckers, and then the root perishes. Other phae- 

 nogamous root-parasites also first attack the exterior of roots. Mr. 

 Bowman has clearly explained in the ' Linnean Transactions' the 

 mode in which the young Lathraea attaches itself to the roots of hasel 

 and ash ; and Schlauter states, in the ' Annales des Sciences,' that 

 when Orobanche attacks Picris hieracioides, the seeds attach them- 

 selves to the points of the roots of the latter, which swell, and form a 

 base for the parasite. I am inclined to believe that this is also the 

 case with at least one British species, Orobanche minor ; for in all 

 cases where I have endeavoured to trace the connexion between this 

 parasite and the roots of the clover, I have invariably found the 

 former located near the termination of the fibrous roots of the latter : 

 and Vaucher states that the seeds of Orobanche ramosa do not sprout 

 unless they come in contact with the roots of hemp, and that they 

 will even lie inert in the earth for years, except they meet with their 

 proper nidus. 



Notwithstanding this apparent difference in the mode in which 

 the rhizogens and other parasites obtain access to the internal parts 

 of the plants on which they vegetate, they all seem to agree in the 

 depth to which they penetrate in search of nutriment. In Cuscuta, 

 Lathraja, Viscum and Loranthus, the suckers stop at the first layer of 

 completely formed wood, and judging from the figures of Rafflesia in 



