SESSILE SPIKELETS IN ONE-SIDED SPIKES 59 



In an allied genus, Cathestecum (which looks like a 

 diminutive Bouteloua) with but one species in the 

 United States, the spikes consist of three spikelets 

 crowded on the short rachis, the uppermost fertile, 

 the two lower staminate or neuter. The spikes fall 

 as a whole from the axis. 



In Lesson III (page 24) it is stated that the posi- 

 tion of sterile florets in the spikelets is the same in 

 large series of related grasses. In the spikelets so far 

 studied in this lesson the sterile florets are above the 

 perfect one. There is a single exception to this rule 

 in Campulosus, in which the two lower lemmas are 

 well developed but empty, the third fertile, and the 

 upper one to three empty, like the lower. 



In two genera in this group, Spartina and Beck- 

 mannia, the spikelets fall entire. (See Lesson VI, 

 page 44, on exceptions). In Spartina the spikelets 

 are strictly 1-flowered; in Beckmannia they are 

 usually 1-flowered, but sometimes a second floret is 

 developed. 



Throughout we have seen widely different forms, 

 such as Eleusine and Bouteloua, connected by inter- 

 mediate forms like Capriola and Chloris. Such an 

 intermediate between pediceled spikelets, as in 

 Bromus, Poa, and others of Lesson IV, and sessile 

 spikelets, as in the group we are now studying, is 

 found in Leptochloa, in which the spikelets are ar- 

 ranged along one side of the slender rachises, but are 

 borne on very short pedicels. The spikelets of our 

 other genera in this highly specialized group present 



