118 TEST CASES [ch. xi 



TEST CASE XII. ALTERNATE OR OPPOSITE LEAVES 



Here is a familiar pair of contrasting characters, occurring in so 

 many different places in the flowering plants that it is clear that 

 they must be very easily acquired, while sometimes one of the 

 two may be shown by a whole family, as are alternate leaves in 

 the grasses. We have already shown (74) that many or most 

 large families show, somewhere in their make up, exceptions to 

 most of the characters that usually mark the family. Thus in 

 Rubiaceae,^ a very large family, one can find alternate, whorled, 

 anisophyllous, pinnate, and gland-dotted leaves, leafy, and intra- 

 petiolar stipules, dioecious, zygomorphic, and solitary axillary 

 flowers, different male and female inflorescences, male and female 

 flowers so different that at one time they were regarded as 

 separate genera, flowers united in pairs, male flower 4-5-merous 

 with female 8-merous, calyx convolute, imbricate, opening 

 irregularly, with calyculus, with one large sepal, 5-merous in 

 male and 2-merous in female; corolla aestivation descending; 

 stamens united, unequal, 8-12, two only with a 5-merous 

 corolla; anthers opening by pores, or by valves, multilocular, 

 heterostyled, with poflinia; ovary superior, united in pairs, 

 1- 3-5- 4- 6-10- or oo-locular; stigma 10 -lobed; capsule both 

 septi- and loculicidal or circumscissile, berry, schizocarp; endo- 

 sperm none, ruminate; embryo with curved radicle, or with no 

 cotyledons. 



This is a very extensive list of exceptions, but most large 

 families show something of the same kind, whilst even in the 

 small ones divergence, usually just as pronounced as the diver- 

 gences just given, is the common phenomenon, usually showing 

 in them between the first two genera, or in the division into 

 species if there be only one genus. 



It is clear that if one were to combine in a group of plants a 

 number of the "abnormal" characters that have just been given 

 for the Rubiaceae, say alternate leaves with intrapetiolar 

 stipules, dioecism, zygomorphic flowers in male and female 

 inflorescences different from one another, the male 5-merous and 

 the female 8-merous; calyx imbricate with one large sepal, 

 corolla with descending aestivation, united, unequal stamens, 



1 Usual characters decussate entire leaves with interpetiolar stipules; 

 regular flowers in cymes or heads, 5-4-merous ; K usually open ; C valvate or 

 convolute ; A 4-5, epipetalous ; G (2), 2-loc., each with 1- co ovules, style 1 ; fruit 

 various; usually endosperm. 



