Origin of Spore-forms. 39 



adapted for favorable conditions and rapid dissemination of the species 

 uredospores. The third form of spore would probably be developed later 

 in point of time. The aecidiospores were at first just like the uredospores, 

 only produced tier upon tier as required, and the great purpose served by 

 all these different kinds of spores would be to provide a continuous succes- 

 sion of spore- forms aecidiospores in the early spring, when the first rush 

 of growth commences; then uredospores during spring and summer, when 

 tteady growth is maintained ; and finally teleutospores towards the autumn, 

 capable of remaining dormant during the winter and starting the whole 

 series again in the spring by means of prom'ycelial spores. 



The so-called spermogonium does not enter functionally into the present 

 cycle, being a relic of the past and a survival of the time when insects 

 were being catered for by the rust-fungi in order to aid in the distribution 

 of their spores ; but the development of such numerous and varied bright- 

 coloured spore-forms has rendered unnecessary this special form of fructi 

 fication. 



VARIABILITY OF TELEUTOSPORES. 



When the teleutospores in the different genera of rusts are carefully 

 examined, it is often found that there is not only considerable variation in 

 (he size and shape, but the seemingly constant character of the number of 

 cells is departed from. It is not always convenient to record this in a 

 systematic description, and I have selected a few species to give an indi- 

 cation of what is not at all uncommon throughout the Uredineae (PI. XL.). 

 This variability not only shows how the uredospore in each genus might 

 have been derived from the teleutospore, but also how the multicellular form 

 of spore might have originated from the unicellular. Starting with the 

 genus Uromyces, there is no difficulty in showing how the bicellular spore of 

 Puccinia may have originated as in Uromyces orchidearum, U. tricorynes, 

 and U. vesiculosus (Pis. XVI., XVIII., XL.) Then in the genus Puccinia 

 there is not only the unicellular teleutospore or mesospore to indicate its pro- 

 bable origin from the Uromyces, but in addition to the two-celled spore 

 there are three and four celled spores, in which the cells are arranged in a 

 manner suggestive of various genera. The different forms seen in a single 

 preparation of P. dichondrae^ Mont, are shown in Plate XL., and there are 

 at least seven forms met with (i) the unicellular spore, or mesospore, 

 generally with thickened apex, and resembling the uppermost cell of the 

 next form; (2) the typical bicellular teleutospore; (3) the three or four- 

 celled spore, with the cells arranged in linear series, superposed more or 

 less regularly and after the Phragmidium type; (4) a three-celled spore, 

 consisting of one basal cell supporting two longitudinally divided on top, 

 and resembling the Triphragmium type; (5) a three-celled spore, consisting 

 of two basal cells longitudinally divided and a single cell on top, as in 

 Hapalophragmium; (6) a four-celled spore with the two lower superim- 

 posed, and the two upper longitudinally divided; (7) a four-celled ellipsoid 

 spore longitudinally and transversely divided, as in Sphaerophragmium. 

 It is worthy of note (that there are no uredospores in P. dichondrae, but, 

 even in P. hidwigii, where uredospores are present, there is also a con- 

 siderable amount of variation. A two-celled spore is met with here, having 

 the septum longitudinal instead of transverse, and the pedicel in a line 

 with it, as in Diorchidium. P. graminis and P. triticina also show a 

 considerable amount of variation, if large quantities of material are 

 examined. Other genera exhibit variation of a similar kind, and there 

 is a basis here provided for natural selection to work upon, and evolve 

 the various forms which are used to characterize the different genera of the 

 Uredines. 



