PROLIFERATION OF SPIKELETS IN BRITISH GRASSES 



49 



P. X jemtlandica bears florets low in the spikelets, but the sex organs are always sterile 

 in contrast to P. alpina. Seminiferous forms and male fertile florets in the viviparous 

 inflorescences are known in P. alpina. Table 3 gives the main characters to distinguish 

 the two viviparous forms. Figure 6 shows seminiferous P. alpina and viviparous P. 

 X jemtlandica spikelets. , 



Table 3 





Poa X jemtlandica 



Poa alpina var. vivipara 



Leaf sheath 



Persistent 



Very persistent in nature 



Cauline sheath 



Smooth waxy green 



Green with yellow ribs 



Ligules 



Usually all long and pointed 



Upper long and pointed ; lower often 

 blunt 



Leaf blades 



Green, flat, tapering to a point gradu- 

 ally 



(Often glaucous), green; usually folded, 

 narrowing abruptly to a hooded tip 



Uppermost knot 



Covered 



Exposed 



The authorities are not agreed upon any clear glume features that may be used to distinguish the species. 



Fig. 6. A. Poa alpina seminiferous: 1. Spikelet (x 3); 2. floret (x 4*5); 3. floral organs (x 4-5). 

 B. Poa X jemtlandica ; 1. Spikelet (x 3); 2. lower glumes; 3. bulbil and lowest floret; 4. as 3, but 

 lemma removed to show the aborted nature of the sex organs. 



In London, seminiferous P. alpina was constant. Few viviparous plants of these 

 Poae were collected in this investigation, because of their rarity. Three of P. alpina and 

 two of P. X jemtlandica were taken; they survived only one year, but produced viviparous 

 culms. Bulbils of P. alpina var. vivipara bore flowers at the end of the summer in which 

 they were borne and struck, but produced viviparous inflorescences next spring. Exo 

 (1916) reported an exactly similar experience with this variety. Schuster found this 

 variety constant in vivipary, except for occasional ' throw-backs ' as in P. bidbosa, especially 

 on poor soil. 



Seminiferous P. alpina is recorded with chromosome numbers of 2n = 19-46, 40, 

 51-54, 57, 64, 65, 67, 72 and 74 (see Nannfeldt's review (1940)). Apomixis has been 

 demonstrated by Akerberg (1942), Engelbert (1940) and Muntzing (1933, 1940). 



