E UPHORBIA CEAE 



257 



Link is very similar and resembles Rhipsalis in Cactaceae. (2) E. 

 xylopkylloides Brongn. has flattened shoots (cf. Phyllanthus Xylo- 

 phylla, and Epiphyllum in Cactaceae). (3) E. Caput- Medusae L. 

 has a stout stock giving off a number of thinner branches at the top. 

 These are covered with little cushion-like papillae, closely crowded, 

 which are really 1. bases; the 1. proper is undeveloped. Many sp. 

 show this structure. (4) E. matnillaris L. has a thorn in the axil of 

 each cushion (=a metamorphosed infl.-axis). If the cushions, as in 

 the cacti, become 'fused ' we get a ridged stem, as is seen in (5! E. 

 polygona Haw. (cf. Echinopsis cereiformis in Cactaceae), E. grandi- 

 cornis and many others. Most of these sp. exhibit pairs of stout 

 thorns which are the slips, of the abortive 1. By the two horizontal 

 thorns one can tell one of these pi. from a cactus, which has a group of 

 thorns. (6) E. melofonnis Ait- is nearly spherical but ribbed, whilst 

 in (7) E. globosa Sims (cf. Echinocactus) we have an almost perfect 

 sphere. [Cf. Cactaceae, and Stapelia, and compare all these succulent 

 forms with one another. See also Goebel, loc. cit.~\ 



Besides the above, note E. splendens Boj and E. Bojeri Hook., 

 pi. with thick stems and green 1., the latter dropped in the dry season. 



The other chief point of interest in E. is the cyathium, or infl. 

 condensed to simulate a single fl. The resemblance is almost perfect. 

 The general branching of the plant is cymose (dichasial). The partial 

 infl. forms a cyathium by the non-development of its internodes, the 

 absence of the P of the individual fls. and the reduction of each 3 fl. 

 to one sta. There is a perianth-like organ of 5 L, really bracts, 

 and between these are 4 curious horn-like bodies (U-shaped in fig.), 

 which are the combined slips, of the bracts. 

 Then follow a number of sta. arranged with 

 the oldest nearest to the centre and each 

 with a peculiar joint half-way up the stalk. 

 In the middle of the cyathium is a 3- 

 carpelled ovary on a long stalk, usu. ripe 

 for pollination before any sta. ripen. 



That this cyathium is an infl. and not a 

 fl., consisting of a lot of 3 fls., each of 

 i sta., round a single $ , is shown by the 

 centrifugal (cymose) order of ripening of 

 organs, and the joint on the sta. ; at this 

 point in the allied gen. Anthostema, there 

 is a P, which shows that the sta. is really a 

 reduced i fl. 



In E. ^Poinsettia the infl. is rendered conspicuous by the bright 

 red colour of the larger upper bracts. These sp. often cult. orn. infl. 



The fruit explodes when ripe ; the carpels split off from the cenlral 

 axis and open at the same moment. 



Euphorbiaceae('/ > .,5A r . \ncl.Suxaceae}. Dicots.(Archichl.Geraniales; 

 Unisexuales BH. ). 220 gen., 4000 sp., cosmop., except arctic. Few 

 sp. have a very wide range ; the most widely-ranging genus is 

 Euphorbia. Closely related to Geraniales by ihe structure of the 

 gynoeceum, &c., although separated a good deal from the other fams. 

 of the order by the amount of reduction in most of its fls. 



Diagram of central cya- 

 thium of infl. of Euphorbia 

 Peplus L. (after Eichler, 

 modified). 



W. 



