86 Rhodora [Marc 
globose head quite after the manner of the achenes in a Ranunculus. 
This is well shown in the excellent drawing by Mr. F. Schuyler 
Mathews, Plate 45, figure 2. The individual carpels (figure 3) are 
reddish brown, strongly 5-ribbed on the back and 3-ribbed ventrally. 
The stigma is essentially sessile and the beak at maturity very small 
or wanting. Echinodorus, although named by Richard ! and treated 
by several subsequent authors as a section of Alisma, was first 
described as a genus by Engelmann, and was separated from Sagit- 
taria chiefly by its perfect flowers and from Alisma by the fact that 
the achenes are thus arranged in a head and not in a ring. The 
genus has been sustained by the two high authorities, Buchenau and 
Micheli, who have subsequently given monographic attention to the 
Alismaceae. The distinction becomes especially clear when as in 
Professor Buchenau's admirably lucid treatment ? the genus Alisma is 
confined to its more typical species. The marked difference in the 
fruit will be readily apparent if the reader will examine figures 2 and 
10, representing the fruit of Æ. parvulus and Æ. radicans respectively, 
and will compare them with figure 9, showing the fruit of our com- 
mon Aisma Plantago, 
In 1830, some eighteen years before our little North American 
Echinodorus was characterized, a South American plant of identical 
habit from the palm swamps of Brazil was very fully described as 
Alisma tenellum, Mart.3 The carpels of this Brazilian plant were 
described as “4-12, plures ut videtur abortivae, in orbem fere dis- 
positae, attamen minus regulariter et multo minus approximatae quam 
in A. Plantagine” and in a later figure, published in the Flora Bra- 
siliensis by Seubert, the carpels are clearly represented in a single 
ring. This figure accurately redrawn is shown in figure 6 of plate 
45. In 1868 Professor Buchenau‘ in a general recension of the A/s- 
maceae transferred Alisma tenellum to Echinodorus, forming. the new 
combination Æchinodorus tenellus. At the same time he states ë that he 
had found no specific distinctions between this South American plant 
and the North American Æ. parvulus. Micheli® in the most exhaus- 
1Mém. Mus. Par. i. 365 (1815). 
? Buchenau in Engl. & Prantl, Nat. Pflanzenf. ii. Abt. 1, 227-232. 
? Martius acc. to J. A. & J. H. Schultes, Syst. vii. pt. 2, 1600 (1830). 
* Abh. naturw. Ver. Bremen, ii. 21 (1868). 
* Buchenau, l. c., 38. 
6 Micheli in A. & C. DC. Monog. Phan. iii. 48 (1881). 
