1.9''2 . Tjffl5 i^ATtTRALlST. 



These stages are often sharply and dearly defined in the plants com- 

 monly known as Cryptogams. When the spore of a fern germinates, 

 a minute leafy expansion is formed, bearing on its surface the anthe- 

 ridia and archegonia, or male and female reproductive organs. This is 

 the sexual generation ; the CK)sphere contained in the archegonium 

 after fertilization directly developes into the large fern plant, which 

 constitutes the asexual generation, so called because the spores ta 

 which it gives origin are not the direct result of fertilization. In this 

 example the evidence as to th^ organic continuity between the twa 

 generations i-s very apparent. In fungi, polymorphism is supposed to 

 occur to a great extent, but in the majority of cases direct evidence is 

 lacking. 



During early summer a minute fungus may be met with on the' 

 leaves' of corn and grasses, forming long yellowish lines ; it originates 

 in the tissues of the plant, and the cuticle is ruptured as the fungus 

 increases in size. Microscopic examination reveals the presence of 

 numerous subglobose, unicellular, orange -coloured bodies, springing 

 from short colourless threads, from which they readily fall away, and 

 form a yellow powdery mass on the leaf, until removed by wind or 

 rain. This is TricJiobasis ruhigo-vera, now almost universally considered 

 as the first stage of Piiccinia graminis. A few weeks later, a second 

 parasite may be met with on the same plants ; the pustules, or lines, 

 are dark brown, and the spores are two-celled, generally slightly 

 constricted in the middle and tapering to each end, and in addition are 

 furnished with a slender pedicel ; this is Pucdnia graminis. The 

 reasons for considering the two above mentioned as stages of the same 

 plant, are as follows : — In a great many instances the Trichobaah is- 

 succeeded by a Puccinia from the same pustule, or on the same plant, 

 and sometimes, as in P. graminis, pustules are not uncommon showing 

 what appears to be a transition from one stage to the other, some of 

 the spores, so called, being one-celled, and others two-celled. Both 

 kinds of spore germinate readily in a damp atmosphere, on a slide 

 smeared with a little glycerine, yet no one has succeeded in growing 

 Fuecinia from Trichobads spores, or vice versa, nor actually demons- 

 trated the presence of the two kinds of fruit springing from the same ^ 

 mycelial thread ; consequently, juxtaposition and persistent sequence 

 of the same forms are the main factors in the arguments as to their 

 relationship. And it must be remembered that there are many species 

 of £iicci?iia that have no known TricJiobasis, and the latter without the 

 corresponding Puccinia stage. By some it is argued that the two are 

 distinct, may-be parasitic on each other, and inter micro-parasitism is 



