2384 



ORCHIDS 



ORCHIDS 



the labellum is situated on the side of the flower 

 toward the axis of the inflorescence, as shown in Fig. 

 2638; that is, it points toward the apex of the inflores- 

 cence. In a few forms this condition is permanent, but in 

 the greater number of orchids the ovary or axis is vari- 



2631. Cattleya dolosa, a sympodial orchid with terminal inflores- 

 cence and pseudobulbs consisting of several internodes. 



ously bent or twisted so that in the mature flower the 

 labellum is on the side of the flower away from the floral 

 axis or, generally speaking, on the lower side of the 

 flower. 



Of all the floral organs the sepals are the least modi- 

 fied. These comprise the outside whorl in Fig. 2638. 

 The one originally opposite the axis of the inflorescence, 

 but which by reason of the turning of the flower just 

 described usually occupies a position adjacent to the 

 axis or on the upper side of the flower, is known as the 

 odd sepal. By reason of its actual position with refer- 

 ence to the flower, it is sometimes called the upper 

 sepal. The other two, which were originally adjacent 

 to the axis of the inflorescence, are the paired or lateral 

 sepals. In most orchids, the lateral sepals are asym- 

 metrical, but noteworthy modifications occur only in a 

 few genera. Sometimes the lateral sepals are partly or 

 entirely united (Cypripedium, Oncidium). In Masde- 

 vallia, all the sepals are united into a short tube at the 

 base, and expand above into three blades terminating 



in long tails. Occasion- 

 ally, the odd sepal is 

 spurred or saccate (Disa) 

 and very commonly dif- 

 ferences in size exist be- 

 tween it and the lateral 

 sepals. 



Of the members of the 

 second whorl, the two 

 lateral ones are usually 

 petal-like while the one 

 opposite the odd sepal is 

 specially modified, and is 

 known as the labellum 

 (I, in Fig. 2638). In most 

 genera the lateral petals 

 resemble the odd sepal, 

 although minor differences 

 in form, size, and color are 

 of frequent occurrence. 

 This resemblance is most 

 striking when these parts 

 have some unusual form, 



2632. CoBlogyne Cumingii, a as \ Oncidium Papilio in 

 sympodial orchid with terminal ^hich they resemble the 

 inflorescence and pseudobulbs antennae OI an insect, or 

 of one internode. in Phragmopedilum cauda- 



tum, in which they are longcaudate, attaining a length 

 of 3 feet. In some genera, the lateral petals show no 

 resemblance to the odd sepal (Huttonsa, Masdevallia, 

 Achrocha3ne) . Asymmetry of the lateral petals occurs 

 very frequently. 



The odd petal, or the labellum, presents the greatest 

 diversity of form of all the floral organs. Sometimes it 

 is small and inconspicuous (Disa), or it is like the lateral 

 petals (Goodyera) . As a rule, however, it is much larger 

 than the lateral petals (as in Fig. 2637), and often it is 

 the most conspicuous part of the flower (Oncidium, 

 Cypripedium, Odontoglossum Londesboroughianum) . In 

 a few genera the labellum is bifid (Vanda, Listera), but 

 in the greater number of orchids it is evidently three- 

 lobed. One of the most common forms which the 

 labellum assumes is that of a trumpet-shaped 

 tube whose sides are formed by the lateral 

 lobes, while the middle lobe is expanded into 

 a variously shaped blade which is often of a 

 deeper shade than the rest of the flower and orna- 

 mented by crests and ridges and color-markings of 

 various kinds which are thought to be of service to the 

 flower by attracting insects and guiding them to the 

 nectar and hence to the pollen and stigmas. This form 

 of labellum is characteristic of many of the most beau- 

 tiful orchids in cultivation (Cattleya, Lselia, Dendro- 

 bium, Phaius). Frequently the labellum is more or less 

 concave, and in Cypripedium and related genera it has 

 the form of a sac (Fig. 2636) often compared to a shoe 

 as the name "lady's slipper" indicates. In many spe- 

 cies, the labellum is strangely transformed and more or 

 less distinctly segmented into a basal part, the "hypo- 

 chil," and a ter- 

 minal petaloid 

 portion which is 

 then designated 

 as the "epichil." 

 Sometimes the 

 differentiation is 

 carried still 

 further and an 

 obscurely de- 

 fined section, the 

 "mesochil," is 

 recognized be- 

 tween these two. 

 The hypochil is 

 the stalklike, or 

 somewhat con- 

 cave winged part 

 which joins the 

 column. It is not 

 clearly distin- 

 guishable from 

 the foot of the 

 columndescribed 

 below. The mes- 

 ochil is usually 

 provided with 

 two lateral cir- 

 rhous append- 

 ages termed 

 "pleuridia," and 

 a central callus 

 known as the 

 "mesidium" 

 (Phalaenopsis, 

 Stanhopea, Peri- 

 steria, Gongora). 

 (Fig. 2641.) The 

 epichil is the 

 simple or lobed 

 terminal part of 2633 - Grammatophyllum speciosum, a 

 tViplaVipllirm Tn sympodial orchid with lateral inflorescence 

 and pseudobulbous stems consisting of sev- 



COlor ana con- era i t man y internodes and attaining a 

 sistency it USU- height of several feet. 



