338 THE ANATOMY OF WOODY PLANTS 



the pollen of the Abietineae and that of the Ginkgoales. Nor 

 is the similarity confined to the structure of the microspores. 

 It has been pointed out in an earlier chapter that the organ- 

 ization of the wall of the sporangium in relation to the opening 

 mechanism and to its derivation from the fibrovascular structures 

 is practically identical in the Ginkgoales and Abietineae. Finally, 

 the organization of the tracheids of the wood is similar in 

 the case of the two groups under consideration. Pinus seems 

 beyond question, by the possession of short-shoots, the number 

 and organization of its microsporangia and megasporangia, as 

 well as by the structure of its microspores, the general organization 

 of the wood, and, finally, by the absence of true wood parenchyma, 

 clearly allied to the sole surviving genus, Ginkgo. 



Pinus, lastly, presents a very strong claim to primitiveness 

 among the Coniferales by reason of the general presence of short- 

 shoots, such as are usually regarded as the prototypes of the 

 ovuliferous scales of the female cone of the Coniferales as a whole. 

 It follows, on the general principles of anatomy laid down in an 

 earlier chapter, that the genus which still shows vegetatively the 

 structures known as short-shoots is in an excellent position 

 to claim a primitive position among the Coniferales. The absence 

 of short-shoots in the seedling of Pinus is obviously no ground for 

 an argument of any significance against the primitive presence of 

 short-shoots in the genus. Negative evidence furnished by seed- 

 lings is of no value, since only positive testimony in connection 

 with the hypothesis of recapitulation can be accepted as valid 

 in evolutionary argument. We may therefore assume that the 

 presence of short-shoots in Pinus and Ginkgo, as well as many 

 other features of resemblance between the two genera, is an unmis- 

 takable indication of affinity. Further, since short-shoots are 

 very generally assumed to have been the prototype of the ovulif- 

 erous scale in the female cones of the Coniferales throughout, we 

 may infer that the coniferous genus which has manifested these 

 structures as a normal vegetative feature from remote geological 

 times must be a very ancient representative of the Coniferales. 



But we are not by any means limited to a consideration of 

 the general organization of the female cone in inferences regarding 



