•23S2 



oiu-iims 



ORCHIDS 



\l<'rphoii'>gy of Ihr irgitatin /xirts. 



All oifliiils iin^ tvrtMinial herbs which, arrordiiiR to 

 I heir nunle of prowl h, f;\ll into two groups — the mono- 

 ixnlial :unl the syinpo<ii-:iI. 



In the monovHwlial onliids. the growth of the main 

 stem is eontinueii invleliiiitely by the terminal bud. 

 (Figs. 2li24-2G27.) l.,ateral branelies are fretiuently 

 pnHl^ut^^, but they lio not regularly assume the part of 

 the main :i-\is and do not under ordinary eon<iitions 

 exetxHl it in length. The growth of the main stem and 

 its branches may be interru|ited for a time by a jieriod of 

 n\st, but such interruption is not manifested on the stem 

 by the formation of scales ami juvenile leaves when 

 gniwtli is resinned. All leaves are similar. The habit 

 of the monopudiid orchids i.s various. In spite of their 

 indeterminate growth, they do not usually attain great 

 size. This fact is explained by the slow growth of 

 the plants, which often require several months to 

 develop a single leaf. Nevertheless, some of the species 

 attain stately proportions. The climbing species of 

 Renanthera sometimes reach a length of 12 feet or 

 more in greenhouses. 8onie of the vandas, aerides, and 

 angnrcums form handsome plants 1 to 2 feet high and 

 well clothed with long distichous leaves. (Figs. 262G, 

 21)27.) While the.se forms grow into tall leafy plants, 

 others, Uke Phahenopsis, remain almost stemless and 

 posse.ss only a few large fleshy leaves. The extreme 

 reduction is represented by such forms as Polyrrhiza 

 ftinalis, in which the stem is reduced to a mere scaly 

 bud seated on a miuss of tangled green roots which 

 perform the function of photosynthesis. 



In the sjTnpodial orchids, the growth of each shoot is 

 definitely terminated usually after one, rarely after two 

 or more seasons. The development of the plant is con- 

 tinued by buds originating in the axils of the scale- 

 leaves at the base of the parent shoot. (Figs. 2628, 

 2629.) The lower part of each new axis is prostrate at 

 first and often stibterranean and bears only scales. It is 

 known as the rhizome. In many terrestrial orchids of 

 the temperate regions, the lower terminal part of the 

 rhizome forms a tuberous root from whose apex the 



shoot of the next seai^on arises. (Fig. 2630.) In a few 

 symixidial orchids with perennial stems and climbing 

 habits, branches originate in the axils of the stem- 

 leaves (Vanilla). These bear a strong resemblance to 



2626. Acgiacum sup«rbum, to show a monopodial growth. 



2627. Vanda tricolor, a branching monopodial orchid. 



the monopodial orchids, but all the branches as well as 

 the main stem are finally terminated by inflorescences. 



The general habit and ap]>earance of orchid plants 

 depends to a great extent on the nature of the rhizome. 

 When this is long, the plants have a loose straggUng 

 habit (Epidendrum). When it is short, the plants are 

 compact (Masdevallia, Cattleya, Coelogyne). The 

 rhizome may be much branched and give ri.se to numer- 

 ous upright shoots (Sobralia, Cojlogyne, Disa), or it 

 may be simple and give rise to only one shoot annually 

 as in many of our native orchids. In some species, the 

 rhizome assumes suberect or climbing habits (Lycaste). 



The upright part of the axis presents a great diversity 

 of forms which may be grouped in two classes according 

 to the position of the inflorescence. This may be either 

 terminal or lateral. 



In the forms with a terminal inflorescence, the 

 leafy part of the stem may be very short .so that the 

 leaves apijear as a rosette on the ground while the upper 

 part of the stem bears bracts from who.se axils the 

 flowers appear (Goodyera, Orchis rolundifolia, Cypri- 

 pedium acaule), but generally it is more developed and 

 bears a succession of leaves which are gradually reduced 

 to bracts in the upper part (Ilabenaria, Cyjiripedium, 

 Disa, Thunia). In Selenipcdilum and Sobraha, the tall 

 reed-like stems reach a height of 6 to 15 feet antl often 

 form dense thickets. In Vanilla the stems are long, 

 branched, and climbing. In many of the epiphytic 

 forms the stem is thickened into a pseudobulb. This 

 may consist of a single internode which bears one or 

 two leaves at its simimit (Ccelogyne), but more fre- 

 quently several intemodes are enlarged to form the 

 pseudobulb, which is then clothed with leaves at 

 least when young, and later bears the scars of fallen 

 leaves (La'lia, Cattleya, Epidendrum). I'^igs. 2631 

 and 2632 show I hi' two forms of pseudobulb. Some- 

 times the whole stem is more or less fleshy without 



