1893.] MICROSCOPICAL JOURNAL. 189 



Fundus Diseases of the Sugar- Beet. 



By L. 11. PAMMlvI., 



AMES, IOWA. 



[I'roiii Bulletin No. 15, Iowa Agricultural l-'xijcrinictit Station.] 



I. — Bkkt Rcst. 



This disi'iisi' is caused by a funj^us (Uromyces-helii:) ami has 

 long been known in Europe'. Its life history was worked out 

 hy Kuehnin 18G9. 



This, like many otiiers, is characterized l>y iiaving three stages, 

 the aecidio (cluster-cup) stage, the uredo (red-rust) stage, the 

 teleuto (winter) stage. The first or aecidium-stage occurs on 

 the petioles, leaves and stems of " seed beets." In this stage 

 two kinds of spores are produced: in one kind, the spores are 

 contained in tlask-shaped receptacles known as the spermogo- 

 nia. These spores are incapable of germination. The sper- 

 mogonia apjiear somewhat earlier than the cluster-cup itself. 

 The cluster-cup when opened contains chains of orange yellow 

 colored sj)Ores. The spores areso compact in the cup that they 

 are polygonal in outline. They arise from short threads at the 

 base of the cup and are known as basidia. The aecidio-spores 

 germinate under favorable conditions, the tube entering the 

 leaf of a beet tlirough snjall rifts known as stomata. In thw 

 tissues of the leaf a mycelium is formed which develops in the 

 intercellular spaces. The thread sends out small lateral out- 

 growths into the cell known as haustoria which absorb nour- 

 isliment from it. It requires only a short time until the mycel- 

 ium collects in certain places beneath the epidermis, from which 

 there arise short uj)right threads wliich bear small, ou'^-celled 

 sj)iny si)ores, known as uredo-spores. These have small bright 

 spots in the cell-walls wliicl) are perforations through which the 

 germ-tube passes. This tube enters the leafthrough the ei>ider- 

 mis. The uredo-sjiores germinate immediately and spread in- 

 fection to neighboring ])lants. Late in the season another kind 

 of spore is found. It is known as the teleuto-spore. They are 

 one-celled, thick-walled, smooth and of darker color. They 

 have attached to them a short branch known as the pedicel. 

 These spores occur in sori by themselves on the petiole or in 

 some cases with tiie uredo-spores. The winter spores do not 



