GENERAL INTRODUCTION 5 



technically conidia as defined above. \\'itliin tlie seed of a llowering 

 plant there is an embryo, or miniature plantlet ; such embryo is 

 entirely absent from both conidium and spore, hence they are not 

 botanically seeds, although functionally both are exactly equal in 

 value to a seed, in the sense that each is capable, under fa\'ourabIe 

 circumstances, of germination and giving origin to a fungus. 



Soon after the fungi emerged from their primitive aquatic home, 

 and took possession of diy land, they quickly shook off the algal 

 characteristics of their ancestors, and clearly indicated the evolution 

 of a new group of organisms, collectively known as fungi, dis- 

 tinguished from all other large groups constituting the Vegetable 

 Kingdom by their structure and mode of life. Such was tlieir 

 energy and adaptability, that it is important to bear in mind that, 

 numerically, fungi at the present day rank next to flowering 

 plants, and in many portions of the globe far exceed them. For 

 instance, in Great Britain we have just over five thousand species 

 of fungi, a number which exceeds that of our flowering plants, 

 ferns, mosses, hepatics, algae, and lichens all added together. 

 Probably the same ^\'ould be true of many other regions if the fungi 

 were as carefully collected and studied as are the higher forms of 

 plant life. 



In addition to the peculiarity of possessing two or more forms 

 of reproductive bodies — some fungi have more than one form of 

 conidia — many fungi possess the remarkable property of living, 

 or spending one part of their life-cycle on one host-plant, and the 

 remaining portion on another distinct plant. This mode of life is 

 termed Jieteyoecism, and such fungi are said to be hetercecious, 

 or living on different substances during different periods of their 

 growth. This peculiarity is most marked in the fungi termed 

 " rusts," as corn rust, or mildew, as it is sometimes called. 



The common corn rust, Puccinia graminis, illustrates this mode 

 of life, and although the fungus itself is not likely to be known by 

 the reader, yet the general principle may be grasped from an 

 explanation of the cycle of development of this fungus. We will 

 commence with the winter- fruit, which is produced on the fading 

 leaves and culms of wheat and some other grasses. These winter- 

 spores, as usual, require a period of rest before they can germinate, 

 in fact, such spores germinate in the spring following their pro- 

 duction. On germination the \\inter-spores give origin to yet 

 smaller spores, which are drifted about by wind, and those that 

 happen to alight on the young leaves of the barberry [Berheris 

 vulgaris) set up an infection which eventually results in the 

 development of the beautiful structures known as " cluster-cups," 

 on account of the cup-like structures containing the spores. This is 

 the first stage of the fungus, produced in the spring, on barberry 

 leaves. The minute spores produced in the " cluster-cups " are 

 in turn dispersed by wind, and those that alight on the young 



