Aecidia and Aecidiospores. 



CHAPTER V. 



AECIDIA AND AECIDIOSPORES. 



The aecidia, or cluster-cups, as they are often called, are usually 

 brightly coloured, and attract attention not only from their colouration, but 

 from their elegant forms as well. The mycelium derived from the germ- 

 tube of a promycelial spore may first produce its spermogonia, and then 

 proceed to the development of aecidia, or aecidia may be succeeded by 

 aecidia. The spore layers are contained in a receptacle or pseudo-pendium, 

 which is formed from a simple layer of flattened sterile cells. It increases 

 in size by the formation of new cells at its base, and is cup-shaped or 

 cylindrical, rupturing at the apex to allow the escape of the spores. 



The aecidiospores are always unicellular, and are arranged in linear 

 series, arising from densely-crowded, erect hyphae or basidia in basipetal 

 order. The young spores are at first separated from each other, according 

 to De Bary, by sterile, intermediate cells, which are soon, however. 

 absorbed, and this makes it often difficult to prove their presence. From 

 the mode of their formation, from above downwards, the ripe spores are 

 at the top, and readily separate to be blown away, while the young spores 

 become polygonal from mutual pressure, lateral and lengthwise. 



The. spores have usually a colourless membrane, with the exception of 

 those of Gymno sporangium, in which it is usually a deep brown, and in 

 the great majority of species are provided with points, spines, or warts, to 

 make them adhere in order to germinate. The granular contents are 

 coloured, as a rule, with an orange-yellow or orange- red oil, although this 

 also occurs in many uredo and teleutospores. 



Germination takes place as in the uredospores by means of a simple 

 cylindrical germ-tube which enters through the stoma into the interior of 

 the host-plant. At certain weak spots in the membrane germ-pores are 

 formed, which are usually only distinctly visible at germination, owing to 

 the swelling of the membrane at these spots, and through these the endo- 

 spore is protruded in the form of a tube. As the aecidiospore germinates 

 very readily in water, the process of germination can be easily followed. 

 A germ-tube rarely arises from more than one pore, and the contents of the 

 spore gradually pass into it along with the orange-colouring matter, so that 

 the spore is ultimately emptied and the endochrome is towards the 

 extremity of the tube. 



I found aecidiospores of Puccinia tasmanica, from the common ground- 

 sel (Senecio vulgaris), to germinate freely in the manner indicated. They 

 were very plentiful in November, and in a drop of water they began to 

 germinate within a few hours, and soon produced germ-tubes of consider- 

 able length. 



As to the length of time that aecidiospores retain their germinating 

 power there is much difference of opinion. De Bary states that they may 

 retain it for some weeks, while Plowright considers it a matter of hours. 

 Eriksson, on the other hand, found that the spores of Aecidium berberidis, 

 for instance, were very capricious and uncertain in their germination, but 

 there is always the possibility that although the spores do not germinate in 

 water, they may infect a host-plant when brought into direct -contact with 

 the living leaf. 



According to Bolley, the aecidiospores on barberry and other hosts are 

 still capable of germination, even after lying in the herbarium for some 

 time, or being sent through the post. 



