For December, 1921 



801 



Epiphytes, Parasites and Saprophytes 



WILLARD N. CLUTE 



THE great majority of plants are independent species, 

 living in the soil and taking from it, or from the 

 air, the materials of which plant food is formed. 

 There are others, however, which have adopted 

 very different methods of food-getting and being thus 

 out of the ordinary have more than the ustial claims to 

 our attention and interest. One group of considerable 

 size has taken on a number of animal characteristics. 

 The species have lost their chlorophyll, the substance 

 which enables them to make food for themselves, and are, 

 therefore, obliged to live on otlier plants, just as animals 

 do. Some of these actually attack living animals or 

 plants and tearing down their tissues appropriate the 

 material to their own uses. 



Those which attack living things are known as para- 

 sites. They occur in all parts of the world and prey upon 

 a great variety of plants, but are most common, of course, 

 in the tropics. ]\lany are so highly specialized that they 

 are limited to a single host. Certain species live on pollen 

 grains only, others are nearly confined to the ovaries of 

 grasses, and still others are parasitic upon subterranean 

 insect larvae, replacing the tissues of the host with their 

 own tissues and incidentally becoming an article of food 

 much relished by certain savages. There is scarcely an 

 animal or plant that is not attacked by one or more para- 

 sites. Even man, himself, is host for a score or more 

 of different species. Some of these are seldom thought 

 of as plants, especially those that cause ringworm, thrush, 

 and dandruff. The bacteria of disease are of course para- 

 sites, though few people are familiar with the fact that 

 they are plants. Among the more curious parasites that 

 infest plants are the species of rust — thousands in num- 

 ber — which require two different hosts to round out their 

 life histories. The well-known wheat rust begins life on 

 the barberry, the corn rust occurs first on the oxalis, the 

 apple rust is found on the cedar, and the poplar rust 

 originates on the larch. 



By far the greater number of plant parasites are found 

 among the fungi but others are flowering plants. Of the 

 latter it has been estimated that at least twenty-five hun- 

 dred different kinds are to be foimd in dift'erent parts of 

 tlie world. The parasitic fungi are for the most part 

 insignificant in size — the bacteria are the smallest of liv- 

 ing things — but their capacity for harm is out of all 

 proportion to their size and is due to the rapidity with 

 which they mtiltiply. The rusts, smuts, mildews, blights 

 and rots that attack common plants are either bacteria or 

 closely allied plants. The parasitic flowering plants, on 

 the other hand, are often of considerable size: in fact, 

 the Rafflesia, a parasite upon various large lianas of the 

 East Indies, has a flower more than nine feet in circum- 

 ference — quite the largest flower in the world. Most of 

 the parasitic flowering plants are parasitic upon other 

 flowering plants, but the Indian pipe is said to reverse 

 the usual condition and become parasitic upon a fungus. 

 There are a few fungi, also, that are parasitic upon other 

 fungi. 



.\s a result of their peculiar life habits, the structure of 

 parasites is often greatly altered. In the flowering ])lants, 

 for instance, the leaves are very small or ab.sent and have 

 no chlorophyll. Often the stem is short or weak and 

 there is a lack of differentiation in the tissues of the 

 embryo. All complete parasites are pale in hue. or if 

 colored, the color is other than green. One of the most 

 familiar of our finwering plant [>arasites, the dodder, has 



a slender orange-colored stem which looks like a tangle of 

 copper wire amidst the vegetation of its haunts. The 

 embryo of this plant well illustrates the reduction in 

 structure of a parasite. It is so degenerate that it has no 

 seed-leaves or cotyledons. The Indian pipe and the 

 broom-rapes are pale and ghost-like species, the former 

 often called corpse-plant or ghost-flower because of its 

 pale and waxy texture. 



Among the flowering plants some species are only half 

 parasites. They have leaves in which there is more or 

 less green and thus are able to make part of their food. 

 Such species often delude the novice into thinking that 

 they are self-supporting plants, esjiecially when they 

 are growing in soil, but their true nature is revealed by 

 digging them up when the roots are found to be fastened 

 to those of other plants. The mistletoe, on the contrar)-, 

 is one of the half-parasites that grow on the branches of 

 trees and is thus easily recognized. 



All parasites live by tearing down the tissues of their 

 hosts in various ways. Some begin life by germinating 

 on the leaves and stems of plants and find their way into 

 the interior of the plant through the stoniata. Once 

 within, they spread from cell to cell, or the plant body 

 may remain in the intercellular spaces and send sucking 

 organs, haiistoria, into the cells to al)sorb the cell con- 

 tents. The flowering plant parasites seldom enter the 

 host, but instead send haustoria into the plants at every 

 point of contact. 



Parasitism occurs in many plant families, but in some it 

 is so prevalent as to be essentially a family characteristic. 

 In the broom-rape and mistletoe families practically all 

 the species are parasites. The figwort family has few 

 complete parasites but half-parasites are common. Among 

 the best known are the yellow foxgloves, cow-wheat, 

 lousewort. and painted cup. The orchid and heath fami- 

 lies also contain many parasites and half-parasites. 



It is often a matter of some difficulty to distinguish be- 

 tween the true parasites and tliose species called sapro- 

 phytes which live on dead organic matter. The two are 

 often closely related and there are certain curious forms 

 which are facultative parasites and may begin life as 

 sapro])hytes but, spreading to living tissues, ultimately 

 become parasites. There are other saprophytes, also, that 

 cannot become parasites of themselves but which may be 

 induced to become so in the laboratory by feeding with 

 the proper substances, such as dilute sugars, until they 

 get started. In Nature, plants often secrete substances 

 in their cells that hinder parasites from entering. 



Sa|)ro]ihytes abound in most groups of the fungi. 

 .\ninng the bacteria there are probably more saprophytic 

 than jiarasitic forms. The flavors of butter, cheese, sour 

 kraut, tobacco, and many other substances are due to the 

 activities of saprophytic bacteria and so are the ptomaines 

 and toxins that occur in nitrogenous foods. All the yeasts 

 are saprophytes and a large number of others are found 

 among the molds, mildews, and sac-fungi. Camembert 

 cheese owes its flavor to a saprophytic mold. .Ml the 

 rusts seem to he parasites. biU among the so-called higher 

 fungi, comprising the earth stars, nuishrooms. pulT-halls. 

 and the like, saprophytes are greatly in the majority. 



.\ considerable number of flowering plants were once 

 thought to be saprophytes, but as the knowledge of these 

 plants has become more exact, most reputed cases of sapro- 

 (ihytism have turned out to be something else: in fact, 

 parasitic or half-parasitic flowering plants outnumber 



