316 LAGENOSTOMALES [CH. 



prolongation of the lagenostome, the micropyle being Uke that 

 in recent Gymnosperms. In Conostoma the tracheid-Uke elements 

 of the lateral wall of the lagenostome are a characteristic feature, 

 and no evidence has been found of the existence of a central core 

 of tissue such as occupies the centre of the seed-apex in Lageno- 

 stoma. The long hairs of Physostoma are represented in Conostoma 

 by the much smaller mucilaginous cells of the epidermis and in 

 Lagenostoma by the less closely united mucilage-cells of the 

 superficial layer of the testa. 



Sphaerostoma. Benson. 



As already pointed out in Chapter xxix. where this genus 

 is described as probably the seed of Heterangium, there is a fairly 

 close general resemblance between Sphaerostoma and Lagenostoma. 

 In the presence of free apical lobes the former genus resembles 

 Conostoma, and while agreeing with Lagenostoma in its annular 

 pollen-chamber it is pecuhar in the retention of an epidermis 

 over the roof of the pollen-chamber : as in Lagenostoma the seed 

 is enclosed by an outer integument or cupule. 



Lagenostoma. Williamson. 



An account of this type of seed is included in the description 

 of Lyginopteris^. The more striking peculiarities are exhibited 

 by the pollen-chamber and the free region of the integument: 

 the annular pollen-chamber (fig. 493, D, c ; fig. 409) surrounds 

 a central nucellar cone and is prolonged upwards as a tube 

 engaging with the micropyle in contrast to the form of the pollen- 

 chamber and the absence of a tubular prolongation in Conostomu. 

 The tentacles of Physostoma and the short apical lobes of Conostoma 

 are replaced by an apical cone formed by the coalescence of the 

 integument containing nine cavities originally filled with paren- 

 chyma (figs. 409 ; 493, B). The presence of a cupule is a character- 

 istic feature of young seeds, but from negative evidence in the 

 case of most other seeds it is unsafe to assume that the cupule 

 of Lagenostoma is an exceptional feature. The nucellus and testa 

 are united as far as the shoulders of the seed as in the seeds of 

 recent Cycads and in contrast to their lateral independence in 

 Trigonocarpus , Stephanospermum, and other genera. 



» Page 65. 



