A RACE OF FLOWERLESS PLANTS— II. 



THE METAMORPHOSES OF FUNGI 



HOW DIFFERENT FORMS CHANGE INTO EACH OTHER. 



ETAMORPHOSIS, or entire 

 change of form, is a familiar phe- 

 nomenon in insects. The cat- 

 erpillar becomes a chrysalis, the 

 chrysalis a moth. In some birds, 

 the plumage of the adult is very 

 different from that of the young. 

 In many marine animals, the 

 offspring is not like the parent but like the grand- 

 parent ; one form is alternated with another, gener- 

 ation after generation. It is so also in ferns ; there 

 is the inconspicuous sexual generation coming from 

 the spore and the asexual generation, the "fern" 

 as we ordinarily see it, bearing the spores. 



Analogous or similar, or even more complicated 

 cases are frequent among fungi. Most persons are 

 familiar with the yellow, jelly-like balls that occur 

 on cedar-trees in spring and are called "cedar ap- 

 ples" (Fig. i). This is a fungus, and the common' 

 rust on the apple is merely another stage of the 

 same fungus. After the first warm rain in spring, 

 the jelly-like appendages of the cedar apples be- 

 come greatly enlarged, and imbedded in them are 

 spores such as are shown highly magnified in Fig. 

 2. The lower spoi'e in Fig. 2 has germinated and 

 has formed secondary spores. The latter can easily 

 be obtained in large quantities by placing one of 

 the cedar-apples on a saucer containing a little 

 water and covering it with a tumbler. As soon as 

 germination takes place, the secondary spores are 

 scattered in a yellow layer over the saucer. In 

 nature, these spores are carried to an apple or wild 

 crab-apple tree, where they germinate and produce 

 the rust, like that in Fig. 3. The rust appears as 

 yellow spots with black specks on the upper sur- 

 face of the leaf, and clustered cups with a fringed 

 margin as shown magnified in Fig. 4. The cups 

 which appear in late summer are filled with spores 

 of a different kind from the others. They in their 

 turn are carried back to the cedar tree and there 

 produce cedar-apples which live over winter and 

 grow in the spring as before. I found last August 

 an apple tree so yellow with rust that it was con- 

 spicuous half a mile away, and under it was a 

 young cedar tree bearing many old cedar-apples 

 and multitudes of new ones. 



The history of wheat rust is similar but more 



complex. Beginning with the cluster-cup stage, 

 we find it on the barberry, not in fall, but in spring. 

 Fig. 5 is a magnified section through a barberry 

 leaf, showing the black specks like sunken flasks at 

 the upper surface, and the cluster-cups on the 

 lower. This form, when growing, possesses re- 

 markable beauty ; the cups, seated in clusters on 

 red spots, are cream-white wax-like cylinders leav- 

 ing a fringed margin, and are filled with spores. 

 Long before it was understood scientifically, farm- 

 ers were convinced by observation that wheat could 

 become infected with rust from barberry bushes.. 

 This belief was so strong that a law was enacted 

 in Massachusetts in 1755, entitled "An Act to pre- 

 vent damage to English grain arising from Bar- 

 berry Bushes." It was not till more than a hun- 

 dred years later that the connection of the barberry 

 fungus with wheat rust was demonstrated, but since 

 that time the facts have been abundantly veirfied 

 by repeated experiments. 



Briefly stated, the facts are these : The barberry 

 cluster-cup fungus (Fig. 5) appears early in spring on 

 the young leaves. The spores of which the cups are 

 full, are scattered by the wind, being carried with much 

 greater ease than ordinary dust, because they are so 

 much lighter. Many doubtless perish, but some, falling 

 on " good ground " in the shape of wheat, oats and other 

 cereals and grasses, germinate, penetrate the plant, and 

 produce easily a thousand fold or more, not of cluster- 

 cups but of rust spores. Two kinds of spores are 

 formed sooner or later, constituting what farmers and 

 botanists call red rust and black rust of wheat. The 

 red rust comes first, and is characterized by oblong 

 orange-colored spores of a single cell, on stalks which 

 easily fall. Black rust comes later on the same mycel- 

 ium or plant, and often in the same cluster, and is char- 

 acterized by dark colored spores having a partition 

 across the middle, and persistent stalks. Fig. 6 con- 

 tains three spores of red rust and one of black rust. 

 Fig. 7 is a cluster of black rust spores. The red rust 

 spores are rapidly scattered, germinate and produce red 

 rust again, perhaps several generations of it, before the 

 black rust spores appear. The latter are more perma- 

 nent ; they live over winter and in spring germinate, in- 

 fect the barberry bushes and produce cluster-cups again. 



Wheat has three distinct species of rust ; the one 

 just described is called Pticciiiia gramiuis, another Puc- 

 cinia Rtibigo-vcra , and the third, which is commoner on 

 oats than on wheat, is Pnci iiua (oi-oiiata. All three have 



