THE ANGIOSPERMAE 1233 



three bundles. The latter corresponds to our second dorsal type in which 

 the suture continues as a groove along the style, which therefore contains the 

 carpel margins and their vascular bundles, as well as the dorsum. This 

 type is illustrated by the instance of Helleboriis which we have quoted above. 

 Lobing or division of the stigma where it occurs is generally associated with 

 this compound origin. Whether one accepts the evolutionary thesis of 

 Eames or not, the two types exist among hving plants and show that solid 

 and grooved or hollowed styles, unitary or compound stigmas have distinct 

 origins and history. 



We may briefly recapitulate the foregoing argument thus: Stigmas 

 may be either purely ventral, when only the carpel margins are con- 

 cerned, or purely dorsal, when they are formed only at the apex of the 

 carpel; or secondarily dorsal, when both margins and apex are associated 

 in the style, but the stigma is confined to the apex. The last condition may 

 be developed, through intermediary stages, from the first. Styles are 

 usually slender organs but in some Euphorbiaceae {e.g., Astrococcus) they 

 are fantastically enlarged and thickened and the ovaries are hidden beneath 

 them, the group of styles looking like a whorl of carpels. 



When we turn to consider coenocarpous gynoecia we see that the styles 

 may be either free or may share the union of the ovaries to a greater or lesser 

 degree. Where the styles are united, the stigmas may be also united, or 

 may remain free, corresponding usually in number to the united carpels, 

 though sometimes branched or variously lobed. The organ formed by 

 the combined styles is, of course, not the same thing morphologically as a 

 simple style and the use of the same name can be a source of confusion. 

 Whatever name we apply to the compound structure, it is manifestly right 

 that the word " style " should continue to be applied to the primary object 

 of that nature, namely, the style of the single, free carpel. 



Compound styles may be either solid or hollow. If the former, there is 

 almost always one or more strands of conducting tissue leading from the 

 stigma downwards to the placentae, forming a path for the penetration of the 

 pollen tubes. If the compound style is hollow the canal is lined with a 

 secretory layer of conducting tissue and this is the path which the pollen 

 tubes follow. One cannot say definitely which condition is the primary 

 one. Schleiden believed that all compound styles were originally hollow, 

 but that the hollow became filled with conducting tissue. This is true of 

 many cases, notably of Anagallis. Joshi on the other hand claims that in 

 solid styles the conducting tissue is a continuation upwards of the ventral 

 (marginal) bundles of the ovary wall and concludes that primitively the 

 pollen tubes followed the course of these bundles and their placental 

 branches, towards the ovules. Generally the two bundles, or the conducting 

 strands arising from them, unite upwards, so that there is a single axial 

 strand in the style. The canal of the hollow style is supposed by him to have 

 originated from this axial strand. 



The conducting tissue itself is generally composed of rather small thick- 

 walled cells, without intercellular spaces, and it produces the sugars which 



