18971 MICROSCOPICAL JOURNAL. 367 



leaf. With careful focussing under a higher power, mi- 

 nute projections studding the surface of the i^})ores be- 

 come visible, giving them a bristly appearance. These 

 nre the summer or uredospores of a parasitic fungus now 

 desiornMted Pnccinia ruhio-o vera, one of the corn-rusts 

 which occasionally inflict so much damage on cerenl 

 crops. P2iccinia graminis \w\\n:Q.^ i\iQ. wheat; allied spec- 

 ies occasion the orange and scarlet patches of rust seen 

 on the rose, barren strawberry, eye-bright, cow-wheat, 

 sow-thistle, groundsel, thistle, harebell, nightshade, 

 dog's .mercury, and many other native plants. The name 

 uredospore {iiro, "I burn") has reference to the conspicu ■ 

 ons disfigarment and often burnt appearance of leaves 

 attacked by these fungi. Unlike telutospores, the ure- 

 dospore germinates at once if placed on a suitable host, 

 and gives rise to a filament whi(>h penetrates the epider- 

 mis and developes into a mycelium, extending through 

 ihe intercellular passages of the leaf. Uredospores com- 

 monly appear somewhat earlier in the season than telut- 

 ospores, though the two often grow together. 



On gooseberries our readers may sometimes have re- 

 marked a briglit yellow spot about the size of a sixpence. 

 Similar spots occur on the leaves of gooseberry and cur- 

 rant bushes. The lens shows that they consist of a num- 

 ber of small round openings full of orange powder; these 

 Mi'e the cluster-cups and SBcidiospores of ^^cidium grossii- 

 lana. An exceedingly common species, Ai. conipositaruvt, 

 is found on the lower surface of the colt's foot leaf, a 

 jdant abundant on every railway embankment. Plants 

 may possess more than one species of parasite; on the 

 colt's-foot there also occurs a species of Colesporium, 

 and nearly a score of different fungi are stated to take 

 up their quarters on the leaves of the nettle. Each spec- 

 ies of secidiura confines itself, as a rule, however, to 

 plants of a particular family, or even selects its hosts 

 from a single species; thus the secidia of the berberry, 



