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PHYSIOLOGICAL BOTANY. PART II. 



phytes," which also grow on the stems and branches 

 of trees, but do not penetrate their bark or absorb 

 their juices. There are a vast number of cryptogamic 

 plants among the ferns, mosses, and lichens, which 

 are epiphytic, as are also several species of certain 

 phanerogamous tribes. This is particularly the case 

 with those Orchidete which are termed " air plants," 

 whose roots imbibe moisture from the atmosphere as 

 we noticed in art. 39. Among the true parasites, 

 some cryptogamic species live wholly within the plant 

 and may be considered analogous to intestinal worms ; 

 whilst such as are external (both cryptogamic and 

 phanerogamic) may be likened to the ticks and lice 

 which infest animals. Different species are parasitic 

 on different parts of plants as on the root, stem, or 

 leaves. Some of the cryptogamic species are highly 

 destructive to our crops, as those which cause the 

 " smut" and " rust" in corn. It is difficult to as- 

 certain in what manner the impalpable powder into 

 which their sporules disperse is introduced within the 

 very substance of the plants attacked ; but it seems not 

 improbable that it may be imbibed with water by the 

 roots. Some suppose it may be introduced through the 

 stomata, but this is not. so plausible an opinion as the 

 former. All the phanerogamic species except those of 

 the natural order Loranthea? (to which the common 

 misseltoe belongs) are destitute of green leaves ; these 

 organs appearing only in the form of small brown 

 scales without stomata, and incapable of performing 

 the functions of respiration. Hence these plants have 

 a livid and discoloured appearance. They are furnished 

 with suckers which penetrate the bark and absorb the 

 proper juices of the plants on which they grow, and 

 which are always dicotyledonous. It is remarkable, 

 that the flower of largest dimensions hitherto discovered 

 is a parasite of this description. This is the Rajfletia 

 Arnold! (Jig. 159-) whose corolla measures a yard in 

 diameter and is fifteen pounds in weight. It grows in 

 the island of Sumatra upon the woody stems and roots 



