718 



development among endogenous plants. Again, take the independent, 

 sturdy oak, with its roots spreading far and wide in search of nutri- 

 ment, and its hundreds of rings of annual growth, connected with the 

 central system by means of the medullary rays ; compare this with 

 many of its less developed associates among the exogens, the parasitic 

 Clandestina, for example, in the stem of which neither medullary rays 

 nor medullary sheath have been found, and whose nutriment is derived 

 from the juices elaborated by other plants, by means of its own insi- 

 dious roots. Nothing has yet been observed among the rhizogens so 

 utterly opposed to all our notions of structural affinity as these oppo- 

 site examples display; and yet the class has been objected to on the 

 ground that "a remarkable diversity of characters has been sacrificed 

 to an appearance resulting from pai'asitism." But in this very para- 

 sitism there is more real agreement than there is between the various 

 modes in which plants included in other classes procure their nutri- 

 ment; and if, as appears to have been done by Mr. Griffith himself, 

 attempts have been made to thrust into the class plants which really 

 differ from it in every essential character, the fault lies, not with the 

 class, but with those who attribute to it discrepancies from which it is 

 entirely free. 



And first with regard to the parasitism of the rhizogens. This, 

 Mr. Griffith says, " can only be said to be constant in its effects, 

 which are similar to those observed to occur (almost) constantly in all 

 phaenogamous plants which are parasitic on roots ;" and he refers to 

 four different modes of parasitism observable in the plants which he 

 considers to have been included in this class, viz.: 1. That exhibited 

 by Rafflesia, Sapria and Cytinus : 2. That of Balanophora and Phse- 

 ocordylis: 3. That of his own genus Thisraia: and 4. That "said 

 to occur in Pilostyles." Commencing with the group Rafflesiaceae, 

 we will remind our readers of the mode of development exhibited by 

 Rafflesia, as figured by Bauer, and previously described (Phytol. ii. 

 715). This plant is there clearly shown to penetrate the cortical lay- 

 ers of the vine, proceeding from ivithin outwards ; in this particular 

 perfectly agreeing with the mode of growth of the entophytal fungi, 

 and being directly opposed to that of parasitic phaenogamous plants. 

 In this mode of parasitism perfectly agree all the genera included in 

 the order ; namely Rafflesia, Brugmansia, Mr. Griffith's own genus 

 Sapria, Apodanthes and Pilostyles : and with this is most probably 

 combined another peculiarity ; that is, the existence of a subcortical 

 mycelium or thallus, forming, in fact, the vegetative organs of the pa- 

 rasites, from which are evolved the flowers or reproductive organs, 



